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Common EVAP Codes – Car Tools, Tips & Advice

9:54 am car tools, Check Engine Light, EVAP, How To Auto Repair, Mechanics Tools

Evap Hose Leak 1

©  Summary: Car repair blog covering the most common causes of EVAP fault codes which are a major reason for Check Engine Lights to come on. Explanation of the purpose of Evaporative systems and tips on what to look for when trouble shooting EVAP fault codes. With a code reader or scan tool, many times the cause of a car’s EVAP code can be diagnosed without additional car mechanic’s specialty tools. Learn which faults are simple fixes and when help from a car repair manual or a dealer tech on-line may be needed. Related car tool blog linked for “EVAP smoke machine use” when leaks are hard to find.

Evap Hose Leak 2

Visual inspection of ALL hoses is a basic first step to find an EVAP problem.

This car repair blog is on EVAP or evaporative systems which are related to management of fuel vapors. We normally think about harmful emissions coming out of the car’s tailpipe, however we seldom think about raw fuel escaping or evaporating before it can be burned in the engine’s combustion chambers. Excessive emissions from raw fuel can harm the atmosphere and is wasteful. Basically the EVAP system in an automobile helps to prevent fuel from evaporating and escaping into the atmosphere. If fuel vapors are kept in the car’s EVAP system instead of being allowed to vanish (or evaporate) into the air, the vapors eventually get burned in the engine. This is best for the environment, efficiency and our wallets. The car’s computer system monitors the EVAP system to insure it is working as designed. If the EVAP system is not passing certain tests, the CEL (Check Engine Light) will be turned on. The specific fault code stored will help to determine what the problem is. The most common cause of an EVAP code to set is due to a leak in the system. If the gas cap is left off after a fill up, a large EVAP code will be set (P0455 Large Leak). This is so common that many cars will indicate that the gas cap may be loose. The warning will display on the information center in the instrument cluster. Of course if the gas cap is tight and the seal is good, further checking will be required to determine the cause of the fault.

Evaporative system leaks, large or small warrant an inspection of all of the hoses from the engine to the fuel tank. The filler neck should also be checked. The tether or strap that is attached to some gas caps can easily get caught between the cap and seal which may damage the o-ring when the cap is tightened. Some drivers that lean on the gas pump nozzle during fill-up can distort the opening of the filler neck where the gas cap seal contacts. This results in the gas cap seal not to seal properly and it may leak. EVAP hoses around air filter housings may become disconnected when the air filter is being checked during servicing. The CEL will take several trips before coming on if any leak occurs. This is why the light may not come on right away if the car owner or a technician has accidentally disconnected an EVAP hose.

Some leaks in hoses or lines in the fuel tank area may be inaccessible for a visual inspection. The Chrysler Pacifica for example has a common leak caused by a plastic vapor line connection on top of the fuel tank. The plastic line tends to shrink over time and ends up snapping the connection from stress on the passenger side, on top of the fuel tank. The most common way to find this leak is with an EVAP smoke machine. When smoke is pouring off the top of the tank the technician is prompted to lower the fuel tank and pinpoint the source of the leak.

EVAP Codes other than leaks…

The most simple EVAP codes to diagnose and repair are ones that have to do with leaks. Large leaks, small leaks etc. Ninety percent of the time, the gas cap will be the cause. More difficult EVAP codes are ones that have to with solenoids and control valves. Purge solenoids sometimes give problems, however it will take more research in a repair manual for the specific model being worked on to determine the problem. Vent solenoids are also a common problem. Many times a vent solenoid could be mistakenly replaced because during a smoke test usually they will be in the vented or open position. Vent solenoids can be commanded to close on some models with a higher end scan tool during smoke testing. Other times the vent solenoid will need to be accessed and closed by energizing it with a power probe or jump wires. The vent solenoid can also be blocked off by manually by kinking a rubber hose prior to smoke testing. The disadvantage of blocking it off manually is that there’s no way to insure that it is closing completely. By commanding it closed or using jumper wires it can be determined if the vent solenoid is closing completely or not. If the vent solenoid does not close all the way when it’s suppose to, a EVAP leak fault would be the result.

Evap Hose Leak 3

Rubber hoses can dry rot over time – they are a major cause of EVAP system leaks.


The easiest fixes for EVAP codes, usually have to do with leaks. Although some leaks can be hard to access, many are rather easy to pinpoint if you know what to look for. A code reader is a great tool for any car owner to have. An inexpensive code reader or scan tool can pay for itself pretty quickly. Car owners with 1996 models and up should look for an OBD II code reader or scan tool. Prior to 1996 EVAP systems are a non issue anyways. Keep in mind that only the higher end scan tools will be able to control solenoids and this function is not available on all vehicles. A smoke machine for detecting EVAP leaks is not really feasible for the car owner but is a great investment for a car repair shop. In fact, most shops can’t effectively work on cars without having access to a good smoke machine. They save a lot of time pinpointing hard to find leaks and this obviously makes the shop more productive. Sometimes mechanically inclined car owners can save money by using a car repair manual on-line or getting help from a dealer tech that knows of common issues with certain models. Be sure to see the valuable links below for more information on code readers. scan tools, on-line repair manuals and to gain insight from a dealer tech that has experience with specific models.

7 Responses
  1. joe :

    Date: June 26, 2014 @ 6:12 am

    Have 2000 s10 2.2 getting a evap leak code p0440 I checked the purge solenoid and its working corectly.. I took the tube and electrical connector off of the vent seonoid by the gas tank and I’m able to blow air into the tube.. Is that normal to be able to blow air through the tube ? Should that hold pressure?

  2. dennisb - Auto Tool Sales :

    Date: June 26, 2014 @ 7:49 am

    The most likely cause of the P0440 code is a vapor leak caused by the gas cap. 99% of the evap leaks are because of a bad gas cap seal or the gas cap being left loose. The vent solenoid is normally in the open position unless commanded closed by the computer. In fact when doing smoke tests the vent solenoid has to be closed off before putting smoke in the system by either manually stopping (plugging or kinking) a hose, commanding it closed with a scan tool or jumping the terminals supplying power and ground. So to answwer your question yes you should be able to blow through the tube and the vent solenoid should only hold pressure when energized. I’d try a new gas cap and clear the code first and go from there. Gas caps are inexpensive and the easiest thing to try. Make sure if purchasing an aftermarket gas cap especially, that it fits properly. Good Luck.

  3. Rona :

    Date: October 22, 2014 @ 4:41 pm

    Hopefully you can give me some advice. I have P0456 and just recently P0442 on. Had a smoke test done when I had the P0456 on and was told “LEAK AT VENT PIPE AT FUEL TANK” and the mechanic also mentioned something about a sending unit. I would like to know what exactly would they be changing or what I should be asking. And if P0442 means the same thing as P0456. I would also like to mention that I went to Chrysler before I got the second opinion/diagnosis and Chrysler just changed the fuel cap. That didn’t solve it and I was surprised they didn’t find the issue. I’m just a lady trying to be more informed. 🙂 Any advice would be greatly appreciated!!!

  4. dennisb - Auto Tool Sales :

    Date: October 22, 2014 @ 6:05 pm

    Hello Rona, the P0456 and the P0442 codes both mean there’s a small Evaporative Emission Control System Leak Detected (very small leak). A gas cap is the most common and least expensive thing to try whenever there’s a small or even a large gas vapor leak. Remember the code won’t immediately disappear just because the cap is installed. The code will take several trips to go off or will need to be cleared with a scan tool or code reader. If the fault remains the code will come back. I would check the mating surface for the fuel cap oring to make sure it hasn’t been made rough from sticking the fuel pump nozzle in the filler neck over time. Some people lean on the fuel pump nozzle when they’re filling up and make the filler neck rough and sometimes egg (oval) shaped. Not common but worth mentioning.

    The shop should do a smoke test with the vent valve closed. There could be a deteriorated hose or other leaks within the system that should be pinpointed when they check properly. A common mistake is to not command the vent closed with the computer or manually before testing. The natural position for the vent valve is open, so it must be closed before the smoke test. As far as the sending unit, the purpose of that is to tell the fuel gauge on the dash how much gas is in the tank. Unless an oring or seal is leaking vapor it doesn’t make sense to replace the sending unit for these codes. Good Luck.

  5. Rona :

    Date: October 23, 2014 @ 3:59 pm

    Thank you for the feedback. I appreciate it.

  6. William :

    Date: November 17, 2014 @ 11:02 am

    I have a 2009 Suzuki Equator with code PO448. When I try to fill tank, after a few seconds, nozzle will cut off and gas gushes back out of filler neck. A local shop has blowed out all the hoses, removed the tank and can’t find the problem. Can you offer any help?
    PS. Engine is 4.0 with auto trans. 44000 miles.

  7. dennisb - Auto Tool Sales :

    Date: November 17, 2014 @ 11:23 am

    You are luck there’s a code to point you in the right direction. The P0448 trouble code means that the Evaporative Emission Control vent solenoid could be closed when it shouldn’t be. Normally the vent is in the open position when the car is off and you are filling the tank. So a bad canister vent solenoid could be the problem. I would see if it can be blown through when the engine is off because it could be stuck closed. If it’s stuck closed, when you fill the tank all that air in the tank ahs no where to go which would result in the overflowing problem that you’re experiencing. Good Luck.

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