Ford P1131, P1151 Fault Codes 3.0 DOHC – O-2 Diagnostics

5:33 pm Apprentice Tech, Auto Specialty Tools, Ford Problems, How To Auto Repair


2003 Ford Taurus with a P1131 oxygen sensor fault code 3.0 DOHC

This automotive repair blog covers a couple of common fault codes that sets the SES (Service Engine Soon) or CEL (Check Engine Light) whichever term you prefer to use. The codes are a P1131 or a P1151, the P1131 is related to B1 S1 (Bank 1 Sensor 1) oxygen sensor which is located near the firewall on the 3.0 DOHC Taurus pictured above. The P1151 is related to the bank that is located near the radiator. There are several probable causes of these codes, we’ll cover the possibilities to help in diagnosing this particular problem.

First a little info on Oxygen (O-2) sensors, first they are located in the exhaust system. An upstream O-2 sensor is located before the catalytic (CAT) converter, while a downstream O-2 sensor is located past the CAT. The purpose of Oxygen sensors is to help the engine run as efficiently as it can which in turn helps reduce emissions. The Oxygen sensors send information to the car’s computer, so it can control the fuel air mixture. The Oxygen sensors normally switch from lean to rich continuously based on the Oxygen content in the exhaust. The reading that was measured in the exhaust is sent to the PCM (Power Train Control Module) – the PCM rapidly changes the fuel mix to optimize efficiency. If the PCM sees that a sensor is not switching as it is expected, a fault code is set and the SES comes on to warn the driver that there is a problem. Lack of switching could be caused by a vacuum leak, a faulty fuel injector, or a lazy (or slow) O-2 sensor. If both, P1131 and P1151 trouble codes are set at the same time, the problem will most likely be attributed to a vacuum leak past the MAF (Mass Air Flow) sensor or something else that would likely affect BOTH banks. If the problem is only causing one code or the other, but NOT both, the problem will most likely be something that would affect one bank, like a bad O-2 sensor or a fuel injector; the most common cause of a single code either the P1131 or P1151 in my experience has been a bad Oxygen sensor.

If P0171, P0174 codes or both have been pulled using a scan tool see our related automotive repair blog for more free tips diagnosing lean codes.
Question – I have a Ford Taurus and want to change the Oxygen sensor that is located in the exhaust manifold on the windshield side. Is it possible to change the sensor without removing the plastic intake manifold to gain access?
Answer– I know it seems buried. The O-2 sensor can be changed by using your left hand to reach from the passenger side of the vehicle down and behind the upper intake. Use an Oxygen sensor socket, a small extension and ratchet… it can be done.

Question – I’ve scanned a P1131 in my VW, does this have the same code definition?

Answer – The P1131 and P1151 can have different meanings depending on the vehicle make. I’ve included definitions for these codes for different manufacturers below.

P1131 and P1151 Code Definitions for the Following Vehicle Makes

Audi – Bank 2 Sensor 1 Internal Resistance too High

Buick – Heated Oxygen Sensor (HO2S) Circuit Low Variance Bank 1 Sensor 2

Cadillac – Heated Oxygen Sensor (HO2S) Circuit Low Variance Bank 1 Sensor 2

Chevrolet – Heated Oxygen Sensor (HO2S) Circuit Low Variance Bank 1 Sensor 2

Chrysler – Fuel Pressure Regulator Valve

Dodge – Fuel Pressure Regulator Valve

Ford – Lack Of Heated Oxygen Sensor Bank 1 Sensor 1 Switches – Sensor Indicates Lean

GMC – Heated Oxygen Sensor (HO2S) Circuit Low Variance Bank 1 Sensor 2

Jaguar – Lack of Heated Oxygen Sensor Bank 1 Sensor 1 switch, sensor indicates lean

Jeep – Fuel Pressure Regulator Valve

Lincoln – Lack Of Heated Oxygen Sensor Bank 1 Sensor 1 Switches – Sensor Indicates Lean

Mazda – Lack Of Heated Oxygen Sensor Bank 1 Sensor 1 Switches – Sensor Indicates Lean

Mercury – Lack Of Heated Oxygen Sensor Bank 1 Sensor 1 Switches – Sensor Indicates Lean

Oldsmobile – Heated Oxygen Sensor (HO2S) Circuit Low Variance Bank 1 Sensor 2

Pontiac – Heated Oxygen Sensor (HO2S) Circuit Low Variance Bank 1 Sensor 2

Saturn – Heated Oxygen Sensor (HO2S) Circuit Low Variance Bank 1 Sensor 2

Subaru – Oxygen sensor circuit malfunction (Short circuit)

Toyota – Air-Fuel Sensor Circuit Range/Performance

169 Responses
  1. Ron :

    Date: July 21, 2009 @ 6:50 pm

    Very usable information. Well put together website and I love the price on the Lisle65600 tool.

    Thanks for your efforts.


  2. John S :

    Date: August 6, 2009 @ 1:12 am

    Thanks for the helpful info on diagnosing Oxygen sensors.
    Great site!

  3. Clinton C. :

    Date: September 30, 2009 @ 10:51 am

    “If both, P1131 and P1151 trouble codes are set at the same time, the problem will most likely be attributed to a vacuum leak past the MAF (Mass Air Flow) sensor or something else that would likely affect BOTH banks.”

    I’m getting both codes on a 2000 SE Taurus. The car is idling terribly. Any suggestions?

  4. dennisb - Auto Tool Sales :

    Date: October 1, 2009 @ 8:42 am

    Clinton, I would check for hissing sounds that may indicate a vacuum leak or an air leak past the mass air flow sensor. Hope this helps. If more assistance is needed, you may want ask a Ford tech on our auto questions page for more ideas.

  5. Torrie White :

    Date: November 16, 2009 @ 3:13 am

    I recently had both P1131 and P1151 pulled on my 2000 Mercury Sable. Everyone knows a Mercury Sable from that year is nothing but a Ford Taurus. I read your comment about the hissing sound and thought to myself, this maybe my problem. It is a great suggestion. I am going to have my car checked for this.

  6. Jac M :

    Date: January 23, 2010 @ 1:25 am

    I have a 98 Sable DOHC. I am getting both P1131 AND P1132. Also, getting a funny smell. Signs pointing to a bad CAT?

  7. dennisb - Auto Tool Sales :

    Date: January 23, 2010 @ 9:19 am

    Jac, rotten egg, propane or burnt rubber smell can be from the catalytic converter. However, the smell alone may not mean that the converter is faulty. Most of the time the smell is caused from excessive fuel entering the exhaust -the catalytic converter’s job is to burn fuel that was not used in the engine; if too much fuel for some reason enters the exhaust, even a good CAT may not be able to keep up. The smell is usually the result of fuel that is unburned in the CAT. The first thing to do is repair the problem that’s causing the fault codes. After the repair, the CAT may not have the smell any longer. Keep in mind that the longer the car is driven with this problem, the more likely that the catalytic converters (your car has two) will be damaged.

  8. cathy :

    Date: February 1, 2010 @ 10:23 pm

    I have a 96 merc,had the intake manifold resealed,check engine light comes on then goes off with a sulfer smell,had p0133,p0151,p1331,p1151,p0171 codes pulled b4 the fix,not sure about cars but i thought reseal would fix the problem,mechanic said it could be just a faulty sesnor I already paid 500 they want 176 more to fix the light any suggestions my emissions are due and i am now broke.

  9. dennisb - Auto Tool Sales :

    Date: February 2, 2010 @ 7:41 am

    Cathy, From what you are telling me, the car may be starting to cost more than what it is worth to maintain.

    1. You may have four oxygen sensors that could be faulty (which most likely would be several hundred dollars alone). Oxygen sensors send a signal back to the computer and they only last so long. The chances of them all being bad at the same time increases the older the car is.

    The sulfur smell you mentioned could be that the car is running rich (at least on one bank). This could be from fuel injectors leaking or oil burning in the exhaust from a worn engine. If the car uses oil and doesn’t seem to leak underneath, it could be burning it.

    It’s also possible the catalytic converters are just about ready for replacement. If they are unable to burn what ends up in them (oil or fuel) the sulfur smell can be present.

    The key is to find a repair shop that will advise you of the over-all condition of the car’s engine and exhaust components. Have them give you a best case scenario (and worst case) so you can decide whether it is worth it to repair this 1996 Mercury or if it’s time to trade up.

  10. dalton :

    Date: February 7, 2010 @ 2:20 am

    i have a 99 Taurus 24v dohc with 212,000 miles and its showing a p1131 and p1132 what would cause it to get a rich and lean code from a just one 02 sensor?

  11. dennisb - Auto Tool Sales :

    Date: February 7, 2010 @ 1:17 pm

    Dalton, Good question – meaning of the codes below.

    P1131 Lack Of Heated Oxygen Sensor Bank 1 Sensor 1 Switches – Sensor Indicates Lean

    P1132 Lack Of Heated Oxygen Sensor Bank 1 Sensor 1 Switches – Sensor Indicates Rich

    Since both codes point to the bank one sensor one oxygen sensor, I would try replacing it. It could be working erratically. Of course with 212,000 miles it could have other issues as well. Like maybe it burns oil when first started and it looks like it’s burning rich? And maybe it has a small intake gasket or other vacuum leak which could cause a lean code? The codes could be triggered at different times and stored.

  12. Chris :

    Date: February 19, 2010 @ 2:44 pm

    I have a 03 Taurus with DOHC and my scanner reads P1131 code. I replaced the sensor by the radiator and the one at the bottom of the engine that is accessed through the passenger side front wheel well. I had to remove a bracket to get the socket on it and then had to grind some the bracket to get it back on. Am I missing one when you say it is located behind the engine by the firewall? The lower one I found was on the passenger side front of the motor. where the belts are. Are there 2 or 3 total?

  13. dennisb - Auto Tool Sales :

    Date: February 19, 2010 @ 4:21 pm

    Chris, The P1131 fault code on the vehicle in the article was fixed by replacing one of the four oxygen sensors. It was (B1 S1) bank 1 which is near the firewall and sensor one which is before the catalytic converter.

  14. Daryl M. :

    Date: March 13, 2010 @ 5:14 pm

    I have a 1998 escort zx2 2.0 and i’m getting 3 codes P1131,P0135 and P0302 any help would be appreciated. thank you.

  15. Harold C Dickerson :

    Date: March 24, 2010 @ 9:16 am

    I have a 2002 ford explorer — the code saids P1151-lack of H0 2S21 switches-sensor indicates lean-can someone tell me where the sensor is located– thanks for the help

  16. dennisb - Auto Tool Sales :

    Date: March 24, 2010 @ 9:29 am

    Harold, o a 4.0 vin “E” P1151 is Bank 2 (driver’s side) Sensor 1 (before catalytic converter.

  17. vinnie :

    Date: March 25, 2010 @ 9:28 am

    95 mercury cougar 4.6 l keep blowing out cat shop doesnt know what their doin p1131now p1132 comes up new coil packs wires spark plugs
    car is sluggish @ 1500 rpm bogs for a sec sometimes smells like rotten eggs shop says fuel pressure is good o2 sensors were ok and all 8 cylinders have good compression mas sensor is new please help they wont warranty my cat anymore its my 3rd one thank you

  18. dennisb - Auto Tool Sales :

    Date: March 25, 2010 @ 10:09 am

    Vinnie, it has to be something that is affecting both banks causing the computer to see LEAN and therefore increasing the fuel mixture. That would cause the converters to be worked excessively to get rid of all the extra fuel ending up in them. Fuel pressure and MASS air flow sensor would be things to look at – you say they have already explored those possibilities. I would look at short term fuel trim while checking for vacuum leaks with carb cleaner around intake gaskets and vacuum hoses, like for the PCV. A vacuum leak makes the most sense from what you are saying. Also if the shop has a smoke machine that can be used to check for vacuum leaks. Another thing to check would be restricted exhaust – with so many failed converters, the muffler could be restricted affecting the readings from the O2’s. If this doesn’t help you may want to ask a FORD tech by visiting our Car Repair Questions section linked at the top of this page.

  19. vinnie :

    Date: March 25, 2010 @ 10:53 am

    thanx dennis for the quick response ill keep ya posted when its fixed maybe i can help others with my same problem im havin ill spray with car cleanear asap i also notice on start up the car idles real bad at first and wants to stall ?? thanks again

  20. dennisb - Auto Tool Sales :

    Date: March 25, 2010 @ 12:38 pm

    Vinnie, Remember the spray is flammable, so be careful around anything that might ignite the vapor (like alternator, coils, etc). Also it is important to watch the fuel trim, with a scan tool, to see if there is a change when checking with the spray around potential leaks. Computers can adjust fuel mix so quickly that sometimes you can’t notice a change in idle even when you are spraying in the “vacuum leak” area.

  21. Harold C Dickerson :

    Date: April 5, 2010 @ 7:52 pm

    Thanks a lot dennisb – appreciate the help

  22. Harold C Dickerson :

    Date: April 10, 2010 @ 9:41 pm

    dennisb – I put sensors on both sides before the cat. now the code is saying p0153 02 circuit slow response bank 2 sensor 1- can you tell me what this mean. Thanks

  23. dennisb - Auto Tool Sales :

    Date: April 12, 2010 @ 9:10 am

    The P0153 code usually means that the B2 S1 oxygen sensor is “Lazy” or slow to respond. I know you replaced it already, so double check to make sure it is the correct part number, also you may want to get an OE one to eliminate the possibilty of the sensor itself being the problem.

    Check for:
    A. Any sign of vacuum leaks, check fuel trim for sign of rich or lean conditions on both banks or if just bank 2 is affected.

    B. Fuel pressure leak down, high or low fuel pressure – however this should affect BOTH banks not just one.

    C. Any exhaust leaks, make sure O-2 is tight.

    D. Mass Airflow – A dirty one may cause this however it more than likely would affect both banks.

    You may also want to ask a Ford tech using the Car Questions page linked at the top of the page.

  24. Harold C Dickerson :

    Date: April 12, 2010 @ 7:00 pm

    Hey dennisb – Thanks again – I kept driving it and the check engine light went off and it’s running smooth – no cut backs or jerks – it’s been running good for 3 days now. Once again thanks!

  25. Dalton :

    Date: May 16, 2010 @ 4:17 am

    this is a response to your reply i replaced the o2 sensor and did some cleaning of the throttle body egr valve etc. and now all that remains is just the p1131 and its now starting to back fire in the inatake/airbox if you give about half throttle from idle and has a surge to it while driving i beggining to think fuel related so i replaced the filter little better but could it be an injector fuel pump any ideas?

  26. dennisb :

    Date: May 17, 2010 @ 12:19 pm

    Dalton, I’m out of ideas as long as you are sure you replaced the correct sensor.

    In that case, you may want to ask a Ford tech on this one by submitting your question on our car question section linked at the top of this page.

  27. Dalton :

    Date: May 22, 2010 @ 12:36 am

    ok thankyou very much for your help

  28. Tex :

    Date: May 24, 2010 @ 4:13 pm

    Great info! I’ve got a 2001 Taurus with error codes 1131, 1151, 0171, 0174, 0136, 0156, and 0300. All of this happened while my wife was driving on the highway. The car won’t idle well (or for long) and it is getting horrible mileage. I’m guessing it’s either a vacuum leak or a bad MAF. Does this sound right? Also, any other suggestions?

  29. Chris :

    Date: June 13, 2010 @ 11:20 pm


    I have a 2000 grand marquis. The car has now power unless I unplug the MAF sensor. My mechanic replaced the MAF sensor and still the same deal. I tried 2 others in case we got a bad one and still the same. he said the fuel pump, and pressure are great. No vacuum leaks that he can find, and he can’t understand why its NOT the MAF sensor. I also tried the EGR valve and the EGR vacuum solenoid and still no luck. If I keep the MAF sensor plugged in I get CODES P1151 and P1131. Any ideas on what it could be? I really hope I can save this car.

  30. J :

    Date: August 5, 2010 @ 2:48 pm

    I have a 2002 Lincoln Navigator. Car was running rough and dying at stops. Error code P0174, P0171. Could not find vacuum leak, changed MAF sensor. Still running bad. Tune-up quote at $700. I changed plugs myself, lot of work. Ran good for two hours than ran worse than before. Error codes P1151, P1131, P0174, P0171. Took intake cover off to check for vacuum leak and heard hissing. Sound coming from PCV end cap on intake. It was split in the back but didn’t look like it from the front. 8 bucks for replacement cap. Running like a champ now.

  31. PatB :

    Date: November 4, 2010 @ 4:51 pm

    How do you get to the spark plugs on the firewall side of the engine?Looks like you have to take off the top intake manifold off.

  32. dennisb - Auto Tool Sales :

    Date: November 4, 2010 @ 6:31 pm

    Upper intake (plenum) removal may be required.

  33. Joe :

    Date: November 7, 2010 @ 10:14 pm

    Hello, i was wondering if you caould tell me where the bank 1, sensor 1 is located on a 1995 lincoln continental. Basiclly i received a P1131 error code after putting in 2 bottles of Techron fuel injector cleaner. i used 2 bottles because the bottle said treats up to 13 gal, i have 18 gal tank. i reset the light and it came back on about 150 miles after. I reset again, and it just came on again around 100 miles later. I cleaned the MAF sensor, but that apparently didnt work. So i guess the o2 sensor is next. Is it hard to replace on my Lincoln?

  34. dennisb - Auto Tool Sales :

    Date: November 8, 2010 @ 7:45 am

    Joe, Usually this code is because of a faulty sensor. Using FI cleaner/additive is not a bad thing, however dirty injectors won’t usually set this code. You may want to ask a Ford/Lincoln dealer tech for the exact location of the sensor and about the degree of difficulty to change it. Changing the wrong sensor would be an expensive mistake.

  35. EdJr :

    Date: December 26, 2010 @ 7:26 pm

    Im out of ideas. I have a 01 Mazda Tribute which is an Escape 3.0L. With codes p1131, p1151, p0136. I drove it with very little gas and it syarted idling rough when cold.
    I replaced the fuel filter, which was very dirty. Didnt fix.
    I replaced the fuel pump, no fix.
    I replaced the spark plugs, same.
    I replace the spark plug wires, no luck.
    I have no vacuum leaks.
    When the heater is on it smells really bad like gasoline. Checked fo leaks, none visible.
    Im out of ideas. Please help?

  36. dennisb - Auto Tool Sales :

    Date: December 26, 2010 @ 8:46 pm

    EdJr, could be bad Oxygen sensors since you don’t have lean codes accompanying the P1131 and P1151. Another possibility could be that when the gas was ran very low like you said that there was some garbage from the bottom of the tank that made it to the injectors. You said the filter was very dirty and that you didn’t have this problem before it ran low on fuel. If the injectors are clogged it’s possible that could trigger lean type codes.

  37. Mike :

    Date: January 3, 2011 @ 3:45 pm

    I have a 2000 taurus DOHC and i am got P1131, P1151, P0174, and P0442 codes. when i start the car on cold days during the winter, the idle isnt right and sometimes it stalls. What would be the problem(s) with the car?

  38. dennisb - Auto Tool Sales :

    Date: January 3, 2011 @ 4:10 pm

    Mike, vacuum leaks when cold could be one of the problems. I would start there.

  39. Mike :

    Date: January 3, 2011 @ 10:47 pm

    I replaced the fuel filter awhile back thinking that was the problem. the idle is not so rough on hotter days. I guess i’ll have to check for a leak

  40. Tasha Blumer :

    Date: February 5, 2011 @ 7:57 pm

    Hello Dennis my name is Tasha and I was wondering if you could loan me some advise. I bought a 99’Mercury cougar last monday from a used car dealer shop. I had it checked before i purchased by a trustworthy mechanic. However today on the freeway i decided to really see how fast my hot cat could go. While pushing 90 on the freeway my check engine light came on. On the way home had it checked and P1151 code was pulled. Should i give the car back or possibly put even more money into a newly purchased vehicle? Thanks for reading, Sincerely Tasha

  41. dennisb - Auto Tool Sales :

    Date: February 5, 2011 @ 8:55 pm


    Problems with any car is a reality. The older the car the more problems you might expect. Don’t blame the trustworthy mechanic. There’s no way for an inspection to find every problem that may crop up. The best case scenario is that the inspection would uncover problems that are present at the time it’s being looked at. As far as the fault code, it most likely would have came on regardless of you seeing how fast she could run! If you like the car are willing to spend on the maintenance and repairs that any 12 year old car will undoubtedly need from time to time… keep it. When we purchase cars we are buying time. The newer the car the more we pay for “time with less trouble.” The older the car, the less we pay initially, with the understanding that we will most likely have more problems to deal with due to the car’s age.

    You may want to ask the car dealer if they would be willing to help you out, on this first problem since you just got the car from them. The squeaky wheel get’s the oil. Of course this will be up to the discretion of the car dealer. Good Luck.

  42. Tasha Blumer :

    Date: February 7, 2011 @ 11:12 am

    Thanks Dennis for your advice I greatly appreciate it. I believe after researching the code it is a O2 sensor that could be faulty but well see. And yes the older cars do need more help but i was hoping a little longer down the road. I love my car but am not mechanically inclined. The dealership also said if i buy the part they will put it in for free so here goes nothing. -Thanks Tasha

  43. Cesar G. :

    Date: March 24, 2011 @ 12:16 pm

    Dennis. I have an Explorer 2002 (with only 50k miles), two weeks ago I was on the Highway in the middle of nowhere when it stopped working. The mechanic said it was the oil pump, end up changing the whole motor ($2500), he also mentioned that the motor now was from an F-250. I drove four hours to pick it up and while we were testing it, we got the P1131 you have mentioned above. The mechanic said it is because a copper tube that goes from the back top of the motor to the lower back of the motor was broken, it was Saturday night and I didn’t want to spend a more days/money trying to get that tube. I drove home, it worked well but the code persists, the problem is that I have no idea what the tube name is as to buy it and change, any suggestions? Thanks

  44. dennisb - Auto Tool Sales :

    Date: March 24, 2011 @ 3:08 pm

    Cesar, not sure about a copper tube. The code P1131 on the Ford means Lack Of Heated Oxygen Sensor Bank 1 Sensor 1 Switches – Sensor Indicates Lean. Maybe call the mechanic and get further explanation or just have a local tech diagnose the Oxygen sensor code and chalk up the “copper tube” thing to miscommunication??

  45. mike doucet :

    Date: April 7, 2011 @ 8:27 pm

    i blew a freeze plug on my 2000 explorer so i replaced it now my engine is running really ruff and im getting codes p1131 and p1151 i knon they say lean bank 1 and 2 but i don’t know what to look for

  46. dennisb - Auto Tool Sales :

    Date: April 7, 2011 @ 9:10 pm

    Mike, I would look for vacuum leaks first. It’s possible though that when the engine overheated, the sensors could have been damaged. Another possibility is that there could be trash or a bug stuck in the mass air flow sensor. I would inspect it to see if there’s any debris which may alter the readings. Good Luck

  47. Matt Kromer :

    Date: April 8, 2011 @ 12:29 pm

    I have 4 codes coming up on my 2003 taurus, p0171, p0174, p1131. p1151. can this all be from one problem like a vaccum leak? and if so is it something that can be done by a DIY-er?

  48. dennisb - Auto Tool Sales :

    Date: April 8, 2011 @ 12:35 pm

    Matt, the most common cause would be a vacuum leak. Some DIY-ers would be able to find a vacuum leak depending upon the severity of the leak. Fast leaks are easy to find and slow leaks (or cold leaks) are more difficult to find. Good Luck.

  49. Matt Kromer :

    Date: April 8, 2011 @ 12:39 pm

    Thanks do you have any tips on finding the leak/leaks?

  50. dennisb - Auto Tool Sales :

    Date: April 8, 2011 @ 12:45 pm

    Matt, there are some tips on the repair blog linked below.

    Pinpointing Vacuum Leaks

  51. Matt Kromer :

    Date: April 8, 2011 @ 12:56 pm

    my car has been idling poorly and has had a lot of trouble starting, (1 out of the past 3 days its started) should make this even more difficult.

  52. dennisb - Auto Tool Sales :

    Date: April 8, 2011 @ 1:38 pm

    Matt, it’s just impossible to say. I recommend reading the article I linked above and then raise the ol’ hood and take a look! Maybe it will be a collapsed hose or a loud hissing vacuum hose if you’re lucky. Good Luck.

  53. Matt Kromer :

    Date: April 17, 2011 @ 10:42 pm

    Well I found a hose with a leak in it. I dont know what its called but it goes from the PCV valve to the intake manifold. I’ve made a makeshift one for now with extra tubing until I can order one from the a dealer. But now codes p1132 and p1152 are coming up. Any advice on those? Also the car is sputtering in idle and almost dies while idling if I turn the heat on. Does this indicate another vacuum leak somewhere else or another problem entirely?

  54. Jerry :

    Date: April 21, 2011 @ 6:44 pm

    Hi dennisb,

    I have a 96 Taurus v6 wagon with just one CAT and one tail pipe. I got the P1131 and online search led me here.

    I read all the comments thus far and I thought I had an idea about where the sensor is. Near the firewall right before the CAT, as oppose to near the radiator. However, I’m now confused after looking at autozone’s diagram:

    In my mind, I thought B1S1 is the bank 1 sensor 2 as labeled in the autozone diagram. Did autozone mislabel it? Because in that diagram B1S1 would be closer to the radiator.

    Please help!



  55. dennisb - Auto Tool Sales :

    Date: April 21, 2011 @ 9:48 pm

    Jerry, The diagram is most likely is right (yours is probably a SOHC). As a way to double check if you are working with the right sensor, you could unplug it and look at the data screen on a scan tool. The default voltage should read .5 Volts when the sensor is unplugged. If you don’t have a scan tool with a data screen, you could unplug it and drive it temporarily to see if a code sets, to verify the sensor and and it’s location. Good Luck

  56. John Eley :

    Date: April 22, 2011 @ 8:48 am

    Hey Dennis I have an 03 Ford Taurus 3.0 DOHC…That recently started idling a little rough (142,000 miles) I had it diagnosed and that cylinder 2 was misfiring. I have just recently replaced all sparks plugs and wires, igintion coil, fuel filter, and air filter, and MAF, needless to say it runs great, however when the car sits idle @ 1000rpm it drops to about 500rpm and back, causing it rough idle… what could this be?

  57. dennisb - Auto Tool Sales :

    Date: April 22, 2011 @ 10:35 am

    John, A compression test may be needed to see if there’s a weak cylinder, since there’s 142,000 mi. But, I would try cleaning the throttle plates and IAC (Idle Air Control Motor). Many times poor or low idle is caused by carbon build up on the throtltle plates. The IAC could also be inoperable, cleaning is something that’s inexpensive to try. Good Luck

  58. Jerry :

    Date: April 25, 2011 @ 2:31 pm

    Dennis, Thank you! Yes, mine is SOHC. I have cleared the code and it’s about over 100 miles now the CEL still hasn’t come on. I monitored the O2 sensors and I have readings on B1S1,2 and B2S1,2. The Sensor 1s get readings soon after the engine starts and the Sensor 2s get readings after the car is warmed up alittle. Does that mean the Sensor 2s are downstream? Well, all sensors’ voltage go up and down at running temp and they look fine to me so far. Can’t really tell which one has triggered the CEL.

    For John, inaddition to Dennis’ suggestion, you might also try adding Engine Restore with your oil changes. My car has 210k miles and it’s running great.

  59. Brad :

    Date: May 10, 2011 @ 10:02 pm

    I am getting P1131, P1151, P0171, P0174, P0316, and PO303 error codes on my 2003 F150 V6. The truck also burns lots of oil and seems to be burning lots of gas lately. Any suggestions?

  60. dennisb - Auto Tool Sales :

    Date: May 11, 2011 @ 8:31 am

    Brad, I would check vacuum hoses particularly the PCV related hoses. If PCV system is not working properly the motor will burn more oil. You could also have worn internal engine components like valves, valve seats, piston rings etc. It’s best to start with simple easy things first though. Need more help? Visit the car questions page and enter your question in the car question box. Good Luck.

  61. Jason Bowen :

    Date: September 10, 2011 @ 1:45 pm

    Hey! I have a 1998 F150 5.4L V8 with 212,000 + miles on it(the odo doesn’t work anymore). It was left sitting upfor a few years and I’ve started working on it. I’ve had to clean the fuel tank, replace the fuel pump and fuel filter. It runs very shaky. When I rev the engine towards 3000 rpm,it feels like it’s about to vibrate away. I pulled a few codes, but haven’t run it long enough to completely go through diagnostics. I have 0141,0156 and 1151. How do I figure out what exactly is going on? I know what the dtc definitions are but how to diagnose?

  62. dennisb - Auto Tool Sales :

    Date: September 10, 2011 @ 2:03 pm

    Jason, all the codes you’ve mentioned are related to Oxygen sensors. Since you’ve had fuel problems from the vehicle siiting up this isn’t surprising. If I were working on it. I would start with new spark plugs and a compression test too while the plugs are out. No sense in throwing a lot of expensive tune up parts at an mechanically worn engine. The compression test will tell you if the engine is too worn to idle properly. Then if the compression is good, I would clear all the codes and see what sticks (which codes return). Hard codes will reset, while soft codes that may have been set when the engine was receiving poor fuel may not return. If possible drive it and see if there are any misfire codes setting and go from there. I wouldn’t be too shocked if the fuel injectors are clogged from contaminated fuel. Good Luck.

  63. John :

    Date: September 27, 2011 @ 9:21 am

    I have a 95 Lincoln continental at 191k now. Engine light been on p1131 took long distance trip month ago and felt slip otw back home. I replaced broken pcv valve, t tube vacuum leak right after pcv valve, MAF sensor, and IAC valve. Car still cuts off when I put it in gear in the mornings. If I put the car in neutral and let it drift a little and put in gear while it’s moving it doesn’t cut off. It was cutting off when I would stop until I fixed the vacuum leak. Could oxygen sensor cause all those problems, I don’t know what else to do. Transmission is brand new from ford with 10k miles on it since I bought it. Please help, I love my car.

  64. John :

    Date: September 27, 2011 @ 9:35 am

    The car also idles high while driving for the first 5-10 mins

  65. dennisb - Auto Tool Sales :

    Date: September 27, 2011 @ 10:19 am

    John, with a high mileage vehicle, I would start by doing a compression test to make sure we are working with a mechanically good engine. If so, an Oxygen sensor is most likely what is needed since you have fixed ALL vacuum leaks. The idle problem may not be related to the Oxygen sensor, but if it’s bad I would replace it and recheck. Good Luck.

  66. John :

    Date: September 27, 2011 @ 10:25 am

    Ok. Would the sensor cause the stalling when I put the car in gear?

  67. dennisb - Auto Tool Sales :

    Date: September 27, 2011 @ 11:11 am

    John, the sensor is not likely to cause your stalling. The computer would use a default voltage if it could not use the actual reading from the sensor. This would be .5V instead of an alternate lean/rich reading that would help the computer adjust the mixture to an optimum fuel strategy. Good Luck.

  68. John :

    Date: September 27, 2011 @ 11:44 am

    Thank you Dennis. Still lil confused but thank you for your time, I really appreciate it. I got my hands full with this one. But at 191k without any previous problems I guess it was due to start acting up at some point.

  69. Matt Kromer :

    Date: September 27, 2011 @ 6:57 pm

    Hi dennis, I have another question about my 2003 ford taurus and I remembered that you were a great source of information. Can you send me your email address, that way I could ask you another question about my power steering this time? I really value your input.

  70. dennisb - Auto Tool Sales :

    Date: October 1, 2011 @ 7:36 am

    Matt, thanks for the compliment. However, I simply don’t have enough time to answer questions unrelated to my blogs (wish I did). Our tool website has been very busy and takes the majority of my time – I’m not complaining. But, since I’m busy, I struggle to keep up with blog comments and I’m sometimes am unable to respond to everyone comments. There are websites that specialize in answering auto repair questions – see our car questions page for information on this. Hope this helps to explain and thanks again for visiting our blog.

  71. John :

    Date: October 4, 2011 @ 10:11 am

    Hey Dennis , I changed the O2 sensor and on the scanner used before still get same description, on different scanner I get air metering description with same code. My MAF is 2 weeks old. Did notice that the MAF was not installed correctly yesterday so I corrected that and reset the PCM. Light not back on yet but cut off when I put it and drive this mourning and at my first stop. I can feel improvement tho but still cutting off. When engine is cold shifting into gear is rough and I know I need a motor mount but what ya think?

  72. dennisb - Auto Tool Sales :

    Date: October 4, 2011 @ 11:18 am

    John, it takes several “trips” for the computer to rest it’s fuel strategy after a repair related to many components especially the MAF (Mass Air Flow) sensor. If the MAF was the problem, there should be an improvement of idle noticed after awhile.

    As a caution to others; it’s really easy to change the wrong O-2 Sensor. If you change the sensor and the same code comes back – you may want to check to make sure the correct sensor was replaced to begin with. Good Luck.

  73. John :

    Date: October 4, 2011 @ 1:31 pm

    Well the egg smell went away and it had gotten pretty bad, I gave the guy at for the code and he gave me the diagram with the picture of which to change. It was pretty black. Ok on the maf I’m gonna change the motor mount and take a trip and test it out. Again though with the stuff I’ve done so far it’s running much better, we’ll see… Will keep you posted of the stalling continues

  74. John :

    Date: October 4, 2011 @ 1:33 pm

    Is there a sure way to test the vacuum system from the vacuum manifold? Visually I can’t find anything else.

  75. dennisb - Auto Tool Sales :

    Date: October 4, 2011 @ 1:56 pm

    Smoke testing with an evaporative type smoke machine like the OTC6521. See our other repair articles on lean codes for more tips.

  76. david :

    Date: October 21, 2011 @ 12:54 pm

    I have a 2001 taurus thats giving me the code p1131, it runs and drives perfect, except when the a/c or heater is on, then it idles VERY rough and sometimes stalls? what is going on? thanks for any help

  77. dennisb - Auto Tool Sales :

    Date: October 22, 2011 @ 8:05 am

    David, if I were working on the car I would make repairs to correct the codes that are set and recheck. If the stalling still persists, I would check for normal suspects… faulty battery, vacuum leaks, IAC (Idle Air Control) motor, excessive carbon build-up on the throttle plate etc. – If the spark plug wires have numbers on them they could be original (10 years old) – a throttle plate cleaning, tune up with a new set of wires could also help some and is needed for maintenance anyways. Good Luck.

  78. THOMAS :

    Date: October 23, 2011 @ 5:06 pm

    Hello…need help! 1995 Lincoln Towncar 4.6 liter. I have irratic idle with codes p1151; p0171; p0174;
    p1131. I can hear a hissing in back where the throttle body connects with the intake manifold. Found a bad hose the connects to the egr valve but I hear a leak but cant see 1. Please help!!!

  79. dennisb - Auto Tool Sales :

    Date: October 23, 2011 @ 6:36 pm

    Thomas, if I were there working on the vehicle I would smoke test it to find the vacuum leak. I suggest you find someone locally with that capability. Once all vacuum leaks are repaired it can be determined if that is the only cause of the codes or not. Good Luck.

  80. Lou :

    Date: December 12, 2011 @ 12:20 am

    Hi Dennis, I have a 2003 Taurus with a standard V6. I have 2 codes, P0174 & P0133. One is the MAF sensor, can I clean that myself? The other is an O2 sensor on Bank 1, I believe that’s on the firewall side of the engine and requires a special wrench to extract. Are there multiple sensors on each Bank? Is Bank 1 all I need to know?
    Thanks, Lou

  81. dennisb - Auto Tool Sales :

    Date: December 12, 2011 @ 6:50 am

    Lou, there are “before cat” sensors and “after cat” sensors on each bank. However, the P0174 most likely means that there’s a vacuum leak affecting the Oxygen sensor’s reading on bank #2. You may want to have a look at our Lean Codes article for more information on this.

    Lean Code’s P0171 and P0174 – Common Causes

    The P0133 trouble code means that oxygen sensor, on bank one sensor one has a slow response time. The P0133 is sometimes accompanied by the P1133 that we discuss in this article. Good Luck.

  82. Jacky :

    Date: December 14, 2011 @ 3:54 pm

    2002 ford explorer … Manufactor code P1151 . Is it going to cost alot to repair? How much parts do I need to repair? My truck shakes when I come to a stop and has a bad gas smell. How much should a mechanic charge?

  83. dennisb - Auto Tool Sales :

    Date: December 14, 2011 @ 4:01 pm

    Jacky, there’s honestly no way I can diagnose your vehicle and provide an estimate through the Internet. I recommend taking the vehicle to a trusted local mechanic, they should be able to provide an estimate after an initial diagnostic fee, typically an hour time their shop labor rate. Good Luck.

  84. SteveH :

    Date: December 26, 2011 @ 8:27 pm

    Wow….great reading…I have a 2000 Ford Contour SE w/a 2.5 duratech thats been comming into the shop with this same code along with a hard code for the B1 S1 O2 sensor…we replaced it about 2 months ago….when I hooked up a scan tool…the voltage read 0 on the sensor….Im wondering if its either the new sensor or if its a wiring issue…..

  85. dennisb - Auto Tool Sales :

    Date: December 27, 2011 @ 6:31 am

    Steve, even with no sensor plugged in the voltage should default to .5 so either you are getting an inccorect reading from the scan tool or you have other issues. Good Luck

  86. Ed :

    Date: January 11, 2012 @ 2:10 pm

    Good read but I’m not sure I have found the problem, 01 ford 350 5.4L, recently having starting issues, sometimes it will not start at all. Yesterday started fine, pulling trailer no issues. Turned off for 30 minutes, has trouble starting, once running check engine light comes on. Driving home, loosing power with each passing mile. Make it home, turn it off. In AM try to start and it just cranks and cranks, codes 0720,0171,0174,P1131

  87. dennisb - Auto Tool Sales :

    Date: January 11, 2012 @ 2:24 pm

    Ed, you most likely have more than one problem going on. The P0720 fault code is the FIRST one I would be concerned with, which is for the output speed sensor. Could be just the sensor or more serious. After that has been taken care of I would check the lean codes which are unrelated to the output speed sensor fault. Good Luck.

  88. Tracie :

    Date: January 19, 2012 @ 10:40 pm

    I have a 1999 Ford Explorer that I purchased last March. The engine light came on 2 days ago, and the car seemed to be struggling when I try to accelerate, but it eventually accelerates. I took it to an auto repair shop so that they could run a test to see why the light came on and they told me that it was the following code that showed up: P1131 (lack of heated oxygen sensor…bank 1 sensor 1…switch indicates lean). The mechanic told me that he turned off the light and that I could probably drive it until the light comes back on. Well, it came back on 30 minutes after I left the shop. I won’t be able to afford to get it fixed for a couple of weeks. Will this mess up my car if I continue to drive it this way? Should I only drive it if necessary?

  89. dennisb - Auto Tool Sales :

    Date: January 20, 2012 @ 6:33 am

    If the light flashes, usually it’s a more serious problem indicating that damage could be done to the catalytic converters. The lack of power you mentioned, may indicate a converter that is already restricting the flow of exhaust (making it difficult to accelerate). It’s always best to do repairs as quickly as possible so problems don’t snow-ball. Good Luck.

  90. Joe Lu :

    Date: February 13, 2012 @ 6:42 pm

    I have a 2001 F150 Lightning. I am getting all four codes – P1131,P1151,P0171,P0174. I’m being told to change all four sensors on my truck but I dont know what the part numbers are or where to buy them, the truck only has 65K miles.
    pls help

  91. dennisb - Auto Tool Sales :

    Date: February 13, 2012 @ 6:46 pm

    Joe, we don’t sell parts. One thing I can tell you is that if I was in your situation I would look for possible vacuum leaks most likely causing the P0171 and P0174 lean codes. Then I would go from there. Good Luck.

  92. Arman :

    Date: March 6, 2012 @ 6:39 pm

    I have a 2002 ford taurus and check engine light came on , code P1131 . Ive noticed its like waisting more gas then it use too. Should i got ahead and change the 02 sensor or should a test it some way first? Please help & thank you.

  93. dennisb - Auto Tool Sales :

    Date: March 6, 2012 @ 6:58 pm

    Arman, most of the time with the code you have, with no other accompanying codes, it’s the Oxygen sensor (like the article covered). An experienced tech with a good scan tool can diagnose/verify this in person if you would like to use a local shop. Good Luck.

  94. Arman :

    Date: March 10, 2012 @ 6:34 pm

    How do i know which 02 sensor to replace if it says sensor 1 bank 1

  95. dennisb - Auto Tool Sales :

    Date: March 10, 2012 @ 7:53 pm

    Arman, S1 (Sensor 1) means the the sensor closest to the engine which is before the catalytic converter. B1 (Bank 1) will be the side of the engine that has the #1 cylinder. Good Luck.

  96. Luvracin :

    Date: April 19, 2012 @ 1:30 pm

    I have a 97 Mercury Tracer and just went to O’reillys and had them test because the check engine light is on. They gave me a big ol’ long list of possibilities but I am pretty sure it’s the O2 Sensor. On the list one of the possible fixes is the sensor in bank 1 sensor 1. So my question is… my spark plugs run along the front of the motor and not down the side so would it still be the sensor before the catalytic converter?? Oh and the diagnostic said my car is running lean… any suggestions on if this is the right sensor? Thank You… so tired of driving with the brake and gas on at the same time at idle…

  97. Luvracin :

    Date: April 19, 2012 @ 1:38 pm

    Oh and 1 more thing would that sensor be considered a downstream or upstream??? Thanks again..

  98. dennisb - Auto Tool Sales :

    Date: April 19, 2012 @ 2:09 pm

    Luvracin, the oxygen sensor before the cat is considered Sensor 1. On 4 cylinder engines there is no Bank 2, only Bank one. And no it doesn’t matter if the engine is sitting straight or sideways. Oxygen sensors are not usually the cause of lean codes, vacuum leaks are. See our repair articles on lean codes for more information. Good Luck.

  99. dennisb - Auto Tool Sales :

    Date: April 19, 2012 @ 2:10 pm

    Sensor 1 is always upstream.

  100. Luvracin :

    Date: April 19, 2012 @ 3:04 pm

    So it’s not the O2 Sensor???

  101. Luvracin :

    Date: April 19, 2012 @ 3:15 pm

    Sorry…The code from O’reillys is p1131..

  102. dennisb - Auto Tool Sales :

    Date: April 19, 2012 @ 3:41 pm

    Luvracin, most of the time with the P1131, there is a bad O2 sensor. Usually that alone won’t cause the vehicle to run rough and hardly idle. You may also have other issues. Good Luck

  103. Luvracin :

    Date: April 19, 2012 @ 4:25 pm

    Ok, thanks for your advice…

  104. Ed :

    Date: June 4, 2012 @ 5:05 pm

    Hi Dennis:

    i own a 97 Ford Tbird with 4.6 eng, have had it for about ten years. Recently “service eng soon” lamp came on, in conjunction to getting a rough idle at startup, which smoothed out by itself after a few minutes. After several driving cycles and not getting the rough idle,the engine light went out [for a day] ,then came back on the next day. I went to local Autozone and they made a complimentary code check, getting P1131. The car has 100,000 miles and i dont put alot of mileage on it now but plan to keep the car. I bought a set of fuel injectors [price was too good to pass up]. If this P1131 is not caused by a bad injector, i need to know what else it might be. O2 sensor i suppose. How would i diagnose it???

    Your help is appreciated.

  105. dennisb - Auto Tool Sales :

    Date: June 4, 2012 @ 5:28 pm

    Ed, the P1131 has nothing to do with fuel injectors. I would look at the Oxygen sensor readings. One DIY method, as long as the sensors are the same is to switch the two, clear the code and see if the fault code follows the sensor. Good Luck.

  106. Jeff :

    Date: June 27, 2012 @ 8:06 pm

    Hey, Dennis. Man, you seem to know it all. I got one for you. I have a 1996 Taurus GL with 158k mi. It’s throwing 1131 & 1151, and when it’s hot outside, I lose power, particularly on a hill. I’ll go down pretty far on the gas, and sometimes nothing, sometimes I can get it to kick into a higher gear with rev near 3000rpm but only a minor increase in power. Then it kicks into a lower gear and rpms and power nearly drop to zero. I can cut it off, wait a few minutes, and it will drive a little better. To top it off, I had my mechanic driving it, we went up a steep hill, it showed all the symptoms (thank God…I didn’t want him to think i was crazy), and when we started to go up the driveway, engine was still on but not enough power–rolling backwards. Hooked up the diagnostic and now it’s showing 3 codes: 1131, 1151, and 0300. This is driving me (and my mechanic) crazy. This happening only when it’s hot outside (coincidence?). Drove fine this morning when it was cool/low humidity. Replaced cam sensor/synchronizer the other day when it was throwing 0340. This problem started before that, though. Did the pcv and fuel filter late last year along with plugs/wires and a couple of other things. My weird problem seems unique. I can’t find it anywhere else. Any help you can give will be greatly appreciated.

  107. dennisb - Auto Tool Sales :

    Date: June 29, 2012 @ 1:48 pm

    Jeff, I have been called a “know it all” before… this time I will take it as a compliment. My first thought would be clogged catalytic converters. The classic symptom of restricted converters is “bogging down” when under load – which could be going up a hill or just trying to accelerate fast. When on a level road and trying to accelerate, backing off sometimes helps the engine to sound better momentarily. This is because the exhaust cannot exit fast enough and is called excessive “back pressure”. We have a tool to check this which is an exhaust back pressure tester. Note, that the other codes may have nothing to do with the no power issue. Good Luck.

  108. Jeff :

    Date: July 1, 2012 @ 6:22 pm

    Thanks, man! You ROCK!

  109. Angilee :

    Date: July 12, 2012 @ 7:28 pm

    My son has a 2002 Mercury Sable and had code P1151 come up. I am trying to figure it out to fix it. It says lack of switches-bank 2 sensor 1. Bank 2 is where as sensor 1 is where on this model of Sable? Also, the tranny hesitates or slow switches from first to second gear. Any help is appreciated and will be heeded.

  110. dennisb - Auto Tool Sales :

    Date: July 13, 2012 @ 8:09 am

    O-2 Sensors locations should be the same as the one in the article. Refer to an on-line repair manual for more information for your specific model. See our repair manual page for info on how to access. As far as the transmission shifting issue, I would check the fluid level, this is the obvious first thing to check. If the fluid is dirty consider a service or better yet, a transmission flush that will change all the fluid in the entire transmission unlike a service that will only change what’s in the pan. Good Luck.

  111. Kathy :

    Date: July 14, 2012 @ 4:52 pm

    I have a 1999 Ford Expedition with almost 228,000 miles on it. Code P-1151 just showed up. From what I read, it can be an oxygen sensor wherever it is or an air leak. Any ideas? thanks

  112. dennisb - Auto Tool Sales :

    Date: July 14, 2012 @ 5:25 pm

    Kathy, most likely an oxygen sensor. God Luck.

  113. Preston :

    Date: July 21, 2012 @ 11:13 pm

    Hi Dennis I have a 97 merc grand marquis that recently had a fault code 1151 and would not pass smog test so instead buying a new 02 sensor I switched the upstream sensors from one side to the other then I cleared the computer drove it a while then I got a fault code of 1131. I suspect it is the 02 sensor but I keep getting conflicting info online and from auto stores . Acording to my manual 1151 code means 02 sensor on bank 2 sensor 1lean And 1131 is bank 1 sensor 1 if bank 1 is on the passenger side cylinder 1 and bank 2 is on the drivers side then switching 02 sensors confirms the 02 is bad . Can you help me on this ?

  114. dennisb - Auto Tool Sales :

    Date: July 22, 2012 @ 8:24 am

    Preston, you are exactly right. I have used this method many times before to verify a diagnosis. I’ve also done this with ignition coils and fuel injectors that were causing codes, but I needed a little more evidence they were bad just to be 100% sure. Good Job!

  115. Preston :

    Date: July 22, 2012 @ 1:23 pm

    Dennis, thank you for the quick reply and your help! I will be bookmarking this page for future references.

  116. Tony :

    Date: July 24, 2012 @ 6:40 pm

    I have a 98′ ford Taurus. got a P1151 code. I’m also smelling burning oil, but it could not be related to this. I’m wondering if this is going to be a costly fix or something I can do at home, the mechanic said there could be a possible gunk build up. I also have ~130,000 miles. Any thoughts?

  117. dennisb - Auto Tool Sales :

    Date: July 24, 2012 @ 6:59 pm

    Tony, it’s likely this article applies to your application (probably just an o-2 Sensor). The oil burning is most likely an oil leak. I would look for leaks. You could pull a valve cover to check for gunk build up. Good Luck.

  118. Molly :

    Date: August 27, 2012 @ 4:47 pm

    Hi, I bought a 2002 Ford Taurus SES a few months ago. The check engine light came on after the first time I filled the car with gas. I took it to AutoZone for a reading and the Troubleshooting code came back P1132: Lack of bank 1 02 transitions-rich.
    What should I do? Could this code be caused by a faulty gas cap?
    Thanks, Molly

  119. dennisb - Auto Tool Sales :

    Date: August 27, 2012 @ 5:27 pm

    Molly, wishful thinking – but no. It most likely has to do with a faulty o-2 sensor like is covered in the article. Good Luck.

  120. Dwayne :

    Date: October 22, 2012 @ 11:58 pm

    hey dennis i have a 1999 lincoln navigator engine shakes at idle also shakes when i’m driving have a sulfer or gas smell coming from the vehcile but i don’t have a check engine on can you give me some advice on what is going on.

  121. dennisb - Auto Tool Sales :

    Date: October 23, 2012 @ 7:08 am

    Dwayne, sulfur and gas smells are distinctively different. A gas smell is going to be from a fuel leak or vapor that is coming from the Evaporative system that handles fuel vapors from the fuel tank and or lines. A sulfur smell from a vehicle can usually be traced back to fumes coming from the battery. If a charging system is delivering too many volts (overcharging) – the acid can be overheated and the acid boiled or vaporized. As far as the shaking, I would check with a scan tool to see if there are any pending codes. Also check mode 6 to see if there are misfires recorded that have not yet reached a high enough number to trigger the engine light/code. Vacuum leaks may cause a shake at idle, but usually will set a lean code. If there is no reason for the engine to shake from the way it is running, it’s possible that motor mounts could be worn. See our other related article on engine shaking.

  122. Toro :

    Date: October 31, 2012 @ 7:01 pm

    I have 1996 Mercury sable 3.0L and the engine overheat when I drive in rush hour on stop and go situation, I changed the thermostat and did a radiator flush and still the same problem. The fan for the radiator works well. It comes on when the temperature goes up, can you give me an idea what can be the problem?


  123. Larry M :

    Date: December 5, 2012 @ 5:51 pm

    I got a question. I have a 03 f 150 and its throwing codes p0174b and p1151. It runs ok in idle but wants to gasp for air when in gear. I have checked and no broken vacuum lines. Need help please.

  124. dennisb - Auto Tool Sales :

    Date: December 6, 2012 @ 12:26 pm

    Larry, I would check the Oxygen sensors. Good Luck

  125. Rick :

    Date: December 6, 2012 @ 1:23 pm

    Both codes 1131, 1151 on 2001 Taurus, was easy-peasy: PCV elbow had gone bad.

  126. dennisb - Auto Tool Sales :

    Date: December 6, 2012 @ 1:40 pm

    Rick, That’s great. I’m surprised the lean codes weren’t also set. It the 1131 and 1151 come back I would suspect O-2 sensors. Good Luck.

  127. Ed :

    Date: January 30, 2013 @ 10:30 am

    I have a ’99 F150 with 65k miles. It recently started throwing the P1131 code. The SES light goes off when I refill the gas tank, and comes back on when the gas gauge reads between 3/4 and 1/2 tank. I don’t notice any performance problems or other changes. Truck was a city vehicle for 12 years and was well maintained.

  128. dennisb - Auto Tool Sales :

    Date: January 30, 2013 @ 10:35 am

    Ed, filling up the tank should have no effect on triggering this code. I would look at the Oxygen sensor. If they are the same you may even swap them and see if the code switches too. This is one way to make sure before spending the money.

  129. Bill :

    Date: March 26, 2013 @ 8:16 pm

    I searched the web for information on the code 1131, found your page and read it carefully. Went to auto parts store, bought a O2 sensor (B1S1) read your instructions about feeling your way back to the sensor, near the firewall and found the sensor. Disconnected the wire, changed the sensor and still had the code… until I disconnected the battery for a few minutes. Code cleared, Check engine is now OUT and we are on the road again. Thanks for a clear and concise description of the problem and solution!

  130. dennisb - Auto Tool Sales :

    Date: March 27, 2013 @ 7:35 am

    Bill thanks for the comment. However, I just wanted to point out that the article is not meant to be a “fix-all”. Most of the time the O-2 sensor will be the problem but not always. And after clearing a code properly with a scan tool (or disconnecting the battery and resetting everything back to factory parameters) the fault could come back. If a fault still exists it will normally take several drive cycles for the computer to do self checks and turn on the CEL (Check Engine Light). Hopefully your problem is solved and the CEL won’t come back on. I just didn’t want our readers to think that this is 100% cure for these codes every-time, because there can be other variables. Thanks again for commenting.

  131. jeffr :

    Date: June 6, 2013 @ 4:05 pm

    I have a 2000 mercury grand marquis. Idles rough and throwing codes all over the place. Have replaced or cleaned several parts but need a new perspective. Multiple codes showing Lean status on both banks, which has also led to cylinder’s 2 and 7 misfiring. Car stutters while driving mostly around acceleration through 40mph. The following codes are in play. P1000, p0136, p1131, p1151, p0171, p0302, p0307. A couple of these showed up twice apparently. I’m figuring a fuel problem. Filter or pump?

  132. lil_krizzy :

    Date: July 4, 2013 @ 4:44 pm

    my sister has a 02 ford escape 3.0 (same motor as all them taurus’). I am getting codes P0135,P0141,P0155 and P0165, they are all o2 heater ciruit codes. I put new sensor in because the car has 150k and they’ve never been done. same codes keep coming back. Fixed all vaccum leaks and inspected wire harness(harness is good) and only slight smell from exhaust. also appearently those codes have been there for a few years. any ideas?

  133. dennisb - Auto Tool Sales :

    Date: July 5, 2013 @ 8:06 am

    Yes, the engines are close to being the same with just a few slight differences. The codes are for heater circuit failure related to the Oxygen sensors located before the catalytic converters. It would make sense if all these codes are caused by one shared problem. It’s possible that there’s a blown 15 amp fuse that powers this circuit. If the fuse is good I would verify that power is reaching the sensors, because there could be break in the circuit (broken wire or bad connection). If the fuse is good and power and ground can be verified at the sensors, I would take a look at the coolant temperature sensor. It can cause problems with the computer’s strategy if the temp being reported is incorrect. Hopefully it’s just a fuse though. Good Luck.

  134. star :

    Date: October 5, 2013 @ 7:44 pm

    Will a o2 senser stop the car from starting on a 01 mercury sable

  135. dennisb - Auto Tool Sales :

    Date: October 5, 2013 @ 7:48 pm

    No. Just not run as efficiently.

  136. Rob :

    Date: March 2, 2014 @ 2:28 am

    Hi been reading over a lot of your posts here…thinking you may be able to help me…I have a 2002 ford Taurus se with 79,000 on it… The car is throwing a code for p1336 “crank shaft position or camshaft position signal to PCM failure”…when I start the car and clear the code and drive it stays off, no mil light…when I stop and let the car fells like it misses and rumbles…(not always easily noticeable or violent) and then throws that code again…and it stays on forever until cleared again…I can then drive 100’s of miles before it returns on after I idol again…ford said that if the crankshaft sensor was bad the car wouldn’t start…so I replaced the cam shaft sensor twice with brand new parts and still no luck! Same code once idling? Any suggestions or thoughts sir?

  137. dennisb - Auto Tool Sales :

    Date: March 2, 2014 @ 9:09 am

    The image is of a different Ford engine but will work as a pretty good illustration.

    Rob, Ford is right only if the sensor had a complete open circuit. The computer would think the engine is not turning so no fuel and spark would be provided. However, the P1336 means that the cam and crank position sensors are out of synchronization. Only the camshaft position sensor can be installed in multiple positions. This is where many people go wrong when installing this sensor. When Ford first made the engine a DIS (Distributor-less Ignition System). They simply used a piece that sat where the distributor used to go. This is now called a cam synchronizer (running off the camshaft). They placed a half moon piece at the top. And a Hall Effect sensor above that to count the revolutions. A common problem is that the 1/2  moon piece becomes distorted. Since there’s not much clearance, it can interfere with cam sensor and ruin it in the process. The computer no longer receives the expected signal, setting off the code. It’s important to install the replacement cam synchronizer in the same clock position, or a code may be triggered again. My guess is that the camshaft synchronizer was NOT installed in the correct clock position. Once this has been removed and installed correctly you should be back in business. Heres the tool used to line it up, click on the image below to see the CAM Sync Tool for the Taurus.

    Ford Cam Synchronization Line Up Tool

  138. Rob :

    Date: March 3, 2014 @ 3:38 pm

    Thank you for your response…I am not ever sure the synchronizer has ever been changed in this car so I picked up a new sensor, synchronizer, and the tool…do you think this will do it? What is the procedure for installing the new parts? Is there anything special I should know? Thank you again for your help!!!

  139. dennisb - Auto Tool Sales :

    Date: March 3, 2014 @ 4:18 pm

    Rob, sorry we couldn’t help you with the tool. I recommend following the repair manual. Good Luck.

  140. Rob :

    Date: March 3, 2014 @ 5:10 pm

    The tool actually came with the new parts and that surprised me! I was sure I was going to have to buy one. Thanks for your help! I cannot find the link?

  141. dennisb - Auto Tool Sales :

    Date: March 3, 2014 @ 7:26 pm

    Oh OK. We no longer have links to the link to online repair manuals but if you Google you’ll find some. Good Luck.

  142. Kezz :

    Date: April 25, 2014 @ 1:53 pm

    Hi. I have a mondeo st 220 53 plate petrol.
    Started having problems with a really bad idle. Garage thought it was the catalytic converters so removed these (as it was cheaper option) and put decat pipes on. This didn’t make any difference, it idles badly and cuts out occasionally when stationary.
    Diagnostic machine brings up codes P0133 and P0153.
    I have changed plugs, leads, coil pack , purge valve, idle control valve, had all pipes checked replaced and cleaned. Have had a new system update and have just had it terracleaned too.
    All this done and still no joy. Mechanics at garage are baffled.
    Any advice would be grateful.

  143. dennisb - Auto Tool Sales :

    Date: April 25, 2014 @ 4:59 pm

    The codes you have are for slow Oxygen sensor response which usually would not cause a drivability issue. It would usually cause the engine to be less efficient and burn more fuel. Since there’s no misfire codes I would check fuel pressure, take a fuel sample to make sure there’s no contaminates like water etc, and check the throttle plate for carbon build up. The throttle plate in the the throttle assembly would not be cleaned with the terraclean decarbonizer you mentioned. You may be getting some more codes saying there’s a catalytic efficiency problem next (if your car has OBD II) In the USA it would have OBD II from 1996 and newer. Good Luck.

  144. Kezz :

    Date: April 26, 2014 @ 7:10 am

    Thanks for your reply, the fuel pressure has already been checked and it’s fine, have also had an emissions test and that was fine too.
    Put the newest IDS system on it and all came up good.
    Totally stuck on what to do next.
    What do you mean by OBD II?

  145. dennisb - Auto Tool Sales :

    Date: April 26, 2014 @ 9:13 am

    In short OBD II is an On Board Diagnostic standard that makes many trouble codes the same throughout the different manufacturers. The standard also mandates that the ECU (Electronic Control Unit) runs self tests on vehicle systems. If certain readings are not within parameters then a trouble code will be triggered. You can read articles on this with a lot more details but that’s the gist of it.

    I recommend doing repairs to get the trouble codes off. Most likely installing new catalytic converters and related Oxygen sensors if needed. Once there’s no fault codes, meaning the systems are all working as designed, the running issues should be taken care of as well. Good Luck.

  146. Clint :

    Date: July 3, 2014 @ 1:19 am

    Hey Dennis, I have a 1998 mercury grand marquis and it’s running less than perfect. I’m showing three DTC’s, they are as follows:
    P1151-lack of Ho2s21 switches sensor indicates lean
    P0133-o2 circuit slow response
    P0156-o2 circuit b2s2

    I replaced both cat converters and all four o2 sensors around 3 months ago using quality parts. And I just recently did a tune up…spark plugs, air filter, fuel filter, oil change… I’m noticing a lack of power on inclines as well as a rough idle.. I’m assuming that these conditions can be caused by the lean condition. I’m trying to see if anyone has dealt with a similar problem before I start tearing into anything. I haven’t checked the MAF as of yet as I know this is a possibility. Any help or advice is greatly appreciated. Thanks man. I look forward to your response as I have been pulling my hair out trying to figure this out.

  147. dennisb - Auto Tool Sales :

    Date: July 3, 2014 @ 10:38 am

    I’d do a compression test on the cylinders. The engine could be tired causing excessive oxygen and possibly unburned fuel to enter the exhaust (and cats). Also it’s possible that the mufflers could be restricted if any internal pieces of the old catalytic converters cam apart. Good Luck.

  148. Clint :

    Date: July 7, 2014 @ 7:50 pm

    Hello Dennis. I recently posted about my 98 grand marquis with the three codes I was getting. Well, I have since resolved that issue and have no engine light on anymore. But I am noticing something strange when I have the throttle about 1/4 of the way open.. My car is making a rattling noise that seems to be coming from the exhaust but I can’t be certain. It’s even more noticeable when traveling uphill and seems to be even more so with the ac on. If I get down on the accelerator it stops making the noise but once the speed has leveled out and I’m back to 1/4 throttle it’s doing it again. Sounds almost like cans in a bag with a little deeper of a tone. Car has 167,000 miles on it. Recently replaced all four o2 sensors and both cats. I’ve been told something about “spark knock” and checking the MAF sensor but I’m not sure if that’s what I’m dealing with as i have no cel present. I’m very much hoping its not the cats I just put on as they were quality parts (or so I think). Any input is greatly appreciated. Thanks.

  149. dennisb - Auto Tool Sales :

    Date: July 8, 2014 @ 7:41 am

    Clint, I’d inspect the exhaust closely to see if it’s been hitting (interfering) with anything on the underside of the car. Keep in mind the motor torquing can shift the exhaust back and forth some, especially if there are worn motor mounts. I’d also take a rubber mallet and tap on the exhaust. This way you can determine if there’s any loose baffles inside the muffler or cats. Finally, the noise could be a spark knock like you mentioned. The spark knock sounds like the timing is off (on older cars). The DPFE can cause this and there doesn’t have to be a code. Good Luck.

  150. marco :

    Date: August 16, 2014 @ 3:37 pm

    Need some help, 99 ford ranger 3.0 flex fuel. Started with the po171 and po174, changed the m.a.f, pcv,checked for vacuum leaks. Brought it back to have the codes read again and along with the previous 2 which are still there it’s now showing 1131 and 1151. I doubt both o2 went bad. Any idea what it might be… dpfe maybe?

  151. dennisb - Auto Tool Sales :

    Date: August 16, 2014 @ 7:27 pm

    Marco, I’d clear the codes and drive it awhile to see what comes back. You could also have it smoke tested depending on what codes are triggered. Good luck.

  152. staten :

    Date: September 25, 2014 @ 7:30 am

    I had a tune-up done now tbe motor is lifting up and the car knocks very bad keeps cutting off. I have a Ford Taurus 1999 3.0 24v can you help me? Now im told its my sensors. I think a mistakes was done.

  153. dennisb - Auto Tool Sales :

    Date: September 25, 2014 @ 7:39 am

    Staten, I would double check the firing order. There should be codes set also. Good Luck.

  154. NateE :

    Date: November 26, 2014 @ 8:12 pm

    Hi Dennis. I have a 2003 F-150 supercab. 6cyl. its showing the following codes,1151,2232,0174, 0171. it is running fine. any ideas on what it is. I have seen several possibilities. I don’t hear any hissing at all either.

  155. dennisb - Auto Tool Sales :

    Date: November 28, 2014 @ 9:36 am

    I would check for vacuum leaks first. You would only hear hissing if there was a huge leak. Good Luck.

  156. knute :

    Date: December 7, 2014 @ 11:19 pm

    Have 1997 merc sable dohc Has 98998 original miles. Just started idling rough and sometimes quits at long stop lights. Took to AutoZone and they ran a free check (hand held unit). Printout says P1151, P1131, P0300, Po156, and P0130. Now going to take to local mechanic (who I don’t know)to get an idea of costs. looked on various parts sites to get an idea but got confusing prices. Am on SS so pricing for repairs is IMPORTANT. If have all this done can you give me a ball park figure at what I can expect or should I try to find another used good deal. Tks.

  157. dennisb - Auto Tool Sales :

    Date: December 8, 2014 @ 7:41 am

    Knute, trouble/fault codes do not tell you which specific parts need to be replaced. They only point you into the right direction. The more codes there are the more difficult finding the problem in many cases. Most of the time there’s not going to be 5 or 6 codes set all at the same time. My guess is that the CEL has been on for awhile, but the car just recently started running bad enough for you to be concerned. As our article indicates the first two codes, P1151 and P1131, are most likely faulty Oxygen sensors. The P0300 is a random misfire code which could be caused by many things, like spark plugs, coils or something like a fuel pump which could affect all at once. Usually the random misfire code is accompanied by specific cylinder misfire codes too, like P0301, P0302, P0303, P0304, P0305 or P0306. The 1-6 in the powertrain codes, indicate which cylinder. It’s strange that one or more of those misfire codes aren’t stored also. The P0156 has to do with the bank 2 sensor 2 Oxygen sensor circuit. It doesn’t necessarilly mean the Oxygen sensor is bad, but that there’s a fault related to that circuit. The P0130 means there’s a fault related to the Bank 1 Sensor 1 Oxygen sensor. This is another code related to an Oxygen sensor which would possibly mean that the sensor is bad or something else could be affecting it’s readings signaling a fault. If I were checking the vehicle I would focuse on the first two codes. Usually the codes that are at the front of the list, when scanned, are the primary codes/faults. I would check the readings with a scan tool to see if the Oxygen sensors are switching properly. I would also consider other factors that could affect them and their readings and how they switched, like vacuum leaks, air intake leak, exhaust leaks etc. For the idle issue, I would also clean the throttle plates and check the IAC (Idle Air Control) motor. Clogged injectors could also be part of the problem, especially if the car sits a lot. I might take a fuel sample if I suspected contaminated or bad fuel. Dirty throttle plates or a carboned up IAC, won’t set a code but are common problems with those rough idle and stalling symptoms. A good tech can give your car a lookover and provide more information. Remember that the parts guy at Autozone, is not really doing any testing, he’s just scanning codes. And while that’s a good free service, it will only take you so far in determining what’s wrong. You get what you pay for. Good Luck.

  158. Wise Auto Tool Blog » Mercury or Ford P1131, P1151, P0300 Codes :

    Date: December 8, 2014 @ 8:21 am

    […] elbows and other vacuum lines. Below is a recent question from a blog reader from our original Ford P1131, and P1151 post from several years […]

  159. fruano17 :

    Date: February 4, 2015 @ 10:47 pm

    On my moms mercury sable 99 im only getting the code P1131 and nothing else would this most likely be just the oxygen sensor or could there be a vacuum leak or air leak as well.

  160. dennisb - Auto Tool Sales :

    Date: February 5, 2015 @ 7:38 am

    Most likely an O-2 sensor but I would still look for vacuum and exhaust leaks. Good Luck.

  161. Gloria :

    Date: February 17, 2015 @ 7:10 pm

    Changed throttle air bypass valve yesterday and now my car is running worse than before. It’s idling rough and there is a slight loss of power when accelerating. Got a code on bank one sensor 2. Can a clogged catalytic converter cause this???

  162. dennisb - Auto Tool Sales :

    Date: February 17, 2015 @ 7:44 pm

    It’s possible depending upon the specific code…

  163. Barry :

    Date: April 26, 2015 @ 9:12 am

    I’ve been reading the posts on this page and you seem like a guy who knows his stuff so I have a question for ya.
    I have a 2001 Ford Taurus, 3.0. 114,000 miles. Recently, check engine light came on. Took it to Autozone to get the code read. Gentleman there said it was the upstream O2 sensor. I bought one upon his recommendation saying I could replace it. I’m having a hard time finding it. Can you give me a better location where to find this at? I replaced something up front that looked like it by the radiator but it ran rougher so I put it back the way it was before. I’m assuming that wasn’t it. If it’s near the firewall, where at specifically?

  164. dennisb - Auto Tool Sales :

    Date: April 26, 2015 @ 9:44 am

    There are two upstream O-2 (Oxygen) Sensors on your car. Even if you replaced the wrong one, it shouldn’t have ran bad if you replaced a good one with a new one unless it’s defective or incorrect for the application. The upstream O-2 sensors are before the catalytic converters, the downstream O-2’s are located after the Cats. Bank one near the firewall and Bank 2 near the radiator. You may be able to follow the wire to it or use a mirror if feeling around doesn’t work. Good Luck.

  165. Barry :

    Date: April 26, 2015 @ 4:30 pm

    thanks for the advice. I replaced the one near the firewall and put the original one back up front but it still runs rough. Not sure on that one.

  166. BKP :

    Date: June 5, 2015 @ 3:48 pm

    Hi, I have a 2002 Ford Taurus with 3.0 DOHC. Has 127,000 miles and no previous major repairs. Also, 3rd time oxygen sensor has been replaced. I’m pretty sure it’s the same sensor replaced each time. I just had MAF sensor replaced 1 week ago. CEL came on next day. Now get read P1131 and gas mileage is worse. Could it be something like CAT causing sensors to go bad?

  167. dennisb - Auto Tool Sales :

    Date: June 5, 2015 @ 5:22 pm

    Maybe the wrong one keeps getting changed. The cat going bad would cause a cat efficiency code. Good Luck.

  168. Jimmy :

    Date: September 11, 2015 @ 8:04 am

    Hey Dennis I have 97 mercury mountaineer it idles in the yard ok but once you start down the road it will only run 20 mph like it’s stopped up can’t hear any vacuum leaks changed plugs and wires coil pack no change it’s reading lean on 1 side and rich on the other not showing abad cat code but what the heck could it be need help

  169. dennisb - Auto Tool Sales :

    Date: September 11, 2015 @ 10:13 am

    Jimmy, lean and rich codes like you’ve described should not prevent the vehicle from going over 20mph. If the RPM’s will increase to 2-3000 RPM’s but the truck doesn’t go over 20 MPH, could be a transmission issue. If it BOGS and sounds choked down, when you try to increase speed, I would test the catalytic converters. There’s a tester that screws into the Oxygen sensor port so you can check pressures before and after each cat. Cat Tester Tool Aid 33600.

Comment Below, Please Unlock Caps

Tell us your thoughts or ask a question. For best results please provide relevant details like your vehicle's year, make, model, engine size, the problem and when it occurs etc. - Comments need to be approved before they are seen by everyone. Notice we don't post Spam. Comment below (*SPAM, ALL CAPS & unrelated comments will be deleted). Click the following to view Dennis' "about page" for info on his background in automotive repair.

Please note: Your comment will not be posted until it's approved. We appreciate and read all on topic, relevant comments. Please don't ask for repair manual info like torque specs, wiring diagrams and specific repair procedures. If quick assistance is needed with purchasing a tool or part, please visit our tool website or call to place an order at 800-524-9783. *Note we don't offer repair advice on the phone.