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Jeep Grand Cherokee Scanned P1281 Fault Code

9:01 am Apprentice Tech, DIY, How To Auto Repair, Jeep, Service Writer


2003 Jeep Grand Cherokee 4.0 Liter Engine with a P1281 Code.

This automotive repair article is on a specific check engine light code for a Jeep Grand Cherokee. When scanned with an automotive scan tool, a P1281 fault code was retrieved. The code has to do with the engine not reaching operating temperature within a certain length of time after the vehicle has been started. For the catalytic converter to operate at it’s best the engine needs to reach it’s normal operating temp. The cooling system’s thermostat normally stays closed when the engine is cold, allowing the motor to warm up quickly. That’s why the trick of removing the thermostat to let the car run cooler, like back in the 1970’s (prior to on-board computers) doesn’t work well anymore.

Back to repairing this specific vehicle. In most cases, a P1281 fault code like the one that caused this CEL (Check Engine Light) to come on; means that the thermostat is either stuck open, or that it has simply fallen apart. In either case it is no longer capable of closing and it cannot stop the flow of anti-freeze throughout the cooling system. This keeps the engine from reaching the normal temperature range within the expected time-frame. When the optimal range is not obtained, the fuel mixture will be too rich, the fuel doesn’t burn as well and catalytic converters aren’t as efficient. Other things can even be affected like the transmission shift points. Shift points may take longer to reach, making the engine wind out more to warm it up sooner.  Jeep_Grand_Cherokee_2003_Thermostat   This thermostat is an easy one to change. As can be seen in the image above, the thermostat came out in pieces. Before installing a new thermostat, the old gasket material must be cleaned one of two ways. 1. With a gasket scraper (old school).  or 2. A roloc type scotch grinding disc and a 90 degree die grinder. Most gaskets for this application have self adhesive backings to help hold them in place. If the gasket doesn’t have adhesive, a little 3M glue can be used to hold everything in place until the bolts can be secured. One mistake made by beginners and by professional techs that get into too much of a hurry,  is to allow the replacement t-stat to fall out of the recess while installing it. If the thermostat housing is tightened up with the thermostat out of position, the housing can be cracked easily. Other than that,  it is a pretty straight forward job. After replacing the thermostat, a Lisle coolant funnel can be used to help burp the air out of the cooling system and fill the over-flow reservoir. Once that is done it’s time to clear the code with a scan tool or code reader.

Question: Is there anything else that could throw a P1281 fault code?

Answer: In most cases it will be due to a bad thermostat, but yes. A faulty temperature sending unit could possibly fool the computer into thinking that the engine did not warm up properly. They have this one worked out pretty well though. The computer is likely to get suspicious of an engine that has been running 20 minutes and still hasn’t reached normal operating temperature.

More about suspected false readings from gauges.

When I suspected a false temperature reading, I would always check with my Genisys scan tool and monitor the data screen. Sometimes there will be two sensors, one for the gauge and one for the computer. I would compare the reading on the data screen and the temperature on the car’s gauge. These readings should be about the same, so if there is a huge difference in the readings then, one is most likely faulty or the gauge itself could be reading inaccurately.

Question: I’m a service writer and many times when I try to get a thermostat covered under an aftermarket warranty the claim is denied. What is the best way to describe the cause and correction to have the best chance of getting this covered?

Answer: I would write this up the following way to provide the information the warranty company needs to make their decision.

Concern: Customer states the CEL (Check Engine Light) is on.

Cause: Scanned P1281, thermostat malfunction indicated. Engine takes too long to reach operating temperature. Verified the thermostat is stuck in the open position – vehicle has no impact damage or aftermarket modifications.

Correction: Installed replacement t-stat and replenished coolant. Cleared code and retested to verify repair and correct concern. 

70 Responses
  1. dennisb - Auto Tool Sales :

    Date: March 7, 2014 @ 11:25 am

    Ruben I would say the codes are not related because they have to do with different systems. If you did not clear the code after replacing the thermostat it will take awhile (several trips as defined by Jeep). The P0455 is usually a bad gas cap seal or because the gas cap was left off completely. Other reasons can be because of rubber hoses deteriorated and leaking in the evaporative system. The P0422 is usually for a catalytic converter that is no longer working sufficiently. Good Luck.

  2. Meredith :

    Date: May 17, 2014 @ 6:58 pm

    I have a 1999 Jeep Cherokee 4.0 with a P1281 code. My scan tool shows this as P1281 Accelerator Pedal Position (APP) Sensor 2 Performance.

    I know you are saying P1281 is too long for coolant to reach operating temperature. Is it possible that for different years the code meant different things?

  3. dennisb - Auto Tool Sales :

    Date: May 17, 2014 @ 8:00 pm

    No, not in this case. Some codes if they are manufacturer specific could mean different things from manufacturer to manufacturer but not within one manufacturer. It’s more likely that your scan tool is just incorrect. There’s a lot of China scan tools that are great. Then there are a lot of China scan tools that aren’t so great especially when they have been backwards engineered to copy another scan tool. I would personally check the thermostat, it’s probably fallen apart. I’ve replaced a lot of these when I worked at Carmax on Jeep Grand Cherokees and regular Classic Cherokees. It’s a common problem which has a very highly documented failure pattern. If you would rather do some more testing before pulling the thermostat you could have the codes checked with another scan tool. Many places will check codes for free or pretty inexpensively. Good Luck.

  4. Jim :

    Date: October 17, 2014 @ 6:49 am

    I have a 2002 Jeep Grand Cherokee that I got codes for bad 02 sensors. I replaced all four and cleared the codes with an OBII diagnosis tool but the codes come back right away. They are all new sensors and installed properly. Wiring and plugs appear good. What can I do to clear the codes?

  5. dennisb - Auto Tool Sales :

    Date: October 17, 2014 @ 7:57 am

    Jim, we have other auto repair articles that are about o2 sensors, this is not one of them. See those O2 articles for more information. Obviously though, O2 codes don’t necessarily mean the Oxygen sensors are bad as you’ve discovered the hard way. The actual codes that your vehicle is setting, are the best clue to what the problem is. If you know the exact codes, research possible causes. Could be an exhaust leak, vacuum leak, a bad catalytic converter etc. Good Luck.

  6. bsaiso :

    Date: January 25, 2015 @ 3:20 pm

    Dear Sir, I bought a 2007 commander Hemi 5.7L, I noticed that there is no red or blue colored lines on the air blowing outlets and it blows cold air when I want warm, I’m confused.

  7. dennisb - Auto Tool Sales :

    Date: January 26, 2015 @ 7:49 am

    The controls are not complicated. So, the heater must not be working. I’d check the heater. Although there can be many reasons, low coolant is the most common cause of the heater not working. Good Luck.

  8. Jessica :

    Date: June 22, 2015 @ 10:02 am

    I have a 04 jeep grand Cherokee lerado, straight 6, 2wd I had recently changed the thermostat in my jeep because when i would turn on my a/c it would over heat my engine (past 210 all the way to max out) Any ways i put in a fail safe 195 thermostat. Ever since I changed my thermostat my temp runs on the line between 100 and 210 while driving, when stopped or parked my temp goes up to 195. well the other night i was taking a long drive on the interstate and my check engine light came on. read code 1281, again my engine was on the line in between 100 and 210 when the light went off… Any answers as to what could be causing this issue?

  9. dennisb - Auto Tool Sales :

    Date: June 22, 2015 @ 10:16 am

    Jessica, I wouldn’t think that a thermostat would have been you problem in the first place, but it most likely is now. I’d try a factory thermostat, since the aftermarket one may not be working as expected. Also make sure that all the air is out of the cooling system and the coolant is full. Good Luck.

  10. Jessica :

    Date: June 22, 2015 @ 10:29 am

    Actually it was, the thermostat was stuck open, and had a leak a small one but still and it was 11 years old (well i think it was, i bought the jeep recently from a private owner). What is the difference between a dealer thermostat and one from auto zone?

  11. dennisb - Auto Tool Sales :

    Date: June 22, 2015 @ 10:43 am

    A stuck open thermostat would not be the cause of an overheat. A stuck open thermostat would cause the engine to NOT reach normal operating temperature in the predetermined parameter that the computer checks, which would result in the code P1281 coming back. You didn’t mention the code or the fact that the thermostat was stuck open, so I assumed that wasn’t the issue you were having. Especially since all I did know was that you were replacing it for an overheat condition which didn’t make sense. The small leak was the main issue for the overheat. The failsafe thermostat is designed to stick in the open position if ever overheated causing the code P1281 to come back. The factory thermostat’s are typically better quality and are designed to open and close at the proper time which would avoid failed tests when the computer does it’s self systems checks.

  12. Jessica :

    Date: June 22, 2015 @ 11:29 am

    Ok there is a misunderstanding here. So it all started with my jeep overheating when i used the a/c, and i didnt have a check engine light. When we changed the thermostat we noticed the thermostat was stuck open didnt even close after being out of the vehicle for over 4 hours, noticed that there could have possibly been a small leak but nothing visible. i changed the thermostat monday 6-15-15, noticed that the jeep would run on the line between 100 and 210 while driving and would slowly go up to 195 while parked or the temp would go up slightly while stopped. saturday night driving 6-20-15 the check engine light came on and gave me the error code P1281. when i have my a/c on the temp does go up a tad from the line between 100 and 210. I checked my ac unit with dye and no leaks. I dont know what else would have caused my jeep to over heat with the a/c on only. again now i have this error code after fixing my thermostat it has not over heated since i changed it. do you know what would cause it. and what is the difference in thermostats from the dealer and one from a part store? and it is that jeep during that time made it to where you can only use a dealer thermostat?

  13. dennisb - Auto Tool Sales :

    Date: June 22, 2015 @ 12:15 pm

    Jessica, there should have definitely been a code if your thermostat was stuck open. You may find an aftermarket thermostat that won’t cause a problem. It’s been my experience that when having thermostat related issues, it’s best go back with the original equipment one from the dealer.

  14. Javier Q :

    Date: July 26, 2015 @ 9:24 am

    Hello Dannis I have the same problem. I have grand cherokee 2002 the code only come on when I drive in the highway. When I drive on the street all working fine. I reset the computer by disconnecting the land wire and after 40 miles driving on the highway the code p1281 come on again. I just changed the thermostat and the code came again

  15. dennisb - Auto Tool Sales :

    Date: July 26, 2015 @ 9:33 am

    Resetting the code does nothing to fix the problem. After the vehicle has been driven long enough for the computer to run self tests and sees a failed one the code will come back and light is turned on. I’d try a factory thermostat and see if that takes care of the problem. Be sure all the air is out of the system and there’s no leaks. Good Luck

  16. Mauricio :

    Date: August 17, 2015 @ 3:35 pm

    Muchas gracias por este articulo

    ..muy explicito he informativo..saludoa

  17. EJ :

    Date: December 21, 2015 @ 10:09 am

    Dennis This blog has been most helpful but one question I was driving maybe 10-15 minutes and noticed Mt cel came on I went to advance auto to scan code came back p1281 which we know is thermostat malfunction but I see that you’ve said it can also be a faulty temperature sending unit as well how do we determine if that’s the case? I don’t want to start throwing parts at my jeep to not fix the real issue….I did notice that after my 15 minute drive from work and letting my jeep idle in the driveway for about 5 minutes it indeed hit 210 on the temp Guage on dash and my fan kicked on so any advice or step by step info would be greatly appreciated thanks

  18. dennisb - Auto Tool Sales :

    Date: December 21, 2015 @ 10:17 am

    Most likely the thermostat. If you wanted to check it first use a scan tool to double check both temp readings. But, I’d replace that first. You’re not talking about a lot of money. Good Luck.

  19. rich :

    Date: January 28, 2016 @ 2:50 pm

    hi I am having the same code and it overheats at idle and I have no heat out of the vents. I replaced the thermostat and had no change. It is a 99 Grand Cherokee and my coolant is now brownish in color, my first thought was a bad head gasket. however, I recently found that I have a cylinder head stamped with casting number 0331. Those stamps are known for having a cracked cylinder head around 100k miles. I have 97k. If you replace the thermostat and still have the issue, I would suggest looking into this known problem.

  20. dennisb - Auto Tool Sales :

    Date: January 28, 2016 @ 3:14 pm

    Rich, If coolant is not getting to the temp sensor the P1281 code can set. I would do a carbon test to see if there’s exhaust in the cooling system, if there is then the head gasket is leaking. The head would be inspected when removed for cracks or pits. Good Luck.

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