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Ron Z.
Ron Z., - Chevy Tech -
Category: Chevy
Satisfied Customers: 19047
Experience:  18+yrs experience. State Inspector and Chevy Diagnostics
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Chevy malibu shows Code PO455 EVAP system leak.

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Hi - I have been driving my chevy malibu 2004 for 6 months with the engine light on becuase I got it checked and was told it would not cause an issue (the sensor that mesures the amount of gas is faulty). Code is PO455 EVAP system leak. I will be needing to do an emissions by summer and will not pass until fixed. What would this entail? Thanks

The P0455 is "EVAP System Large Leak Detected". Very commonly this is a faulty Fuel Cap. Above you stated you replaced the fuel cap- be sure the fuel cap with which you replaced is as close to OEM specs as you can (the fuel caps sold at aftermarket stores like "AutoZone" do not meet OEM specs, and will NOT solve a P0455). If you positive the fuel cap is good, next check the fuel filler neck for any signs of damage or debris that will prevent the cap from sealing correctly. If thius check ok, you can next check around the fuel tank area for any signs of damage and/or broken vacuum lines. If the visual ispection checks ok.then the next best thing to do is to have the EVAP system "smoked". This is where a machine forces smoke through the EVAP system, and the "large leak" will reveal itself with a stream of smoke. Most shops charge around $45-$65 for this service, but it's money well spent, as chasing a leak in the EVAP system can be hard to do, especially if the leak is in a place where you cannot visually see, like say the top of the fuel tank.

Customer: replied 6 years ago.
I would like a little bit more info on the possibilities; I am looking for the diagnostic I did before, but they mentioned something about the difficulty of fixing this do to removing something and other labor costs, can you please tell me the worst case senario. thanks

Here's the diagnostic flow chart provided by GM for the P0455. (Notice the step that says to use a smoke machine. Might be the best bet! The P0455 isn't one of those codes where you can say "Oh, it's this....")

DTC P0455


  • To help locate intermittent leaks, use the J 41413-200 Evaporative Emissions System Tester (EEST) to introduce smoke into the EVAP system. Move all EVAP components while observing smoke with the J 41413-SPT High Intensity White Light. Introducing smoke in 15 second intervals will allow less pressure into the EVAP system. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
  • A temporary blockage in the EVAP canister purge solenoid valve, purge pipe, or EVAP canister could cause an intermittent condition. Inspect and repair any restriction in the EVAP system.
  • To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with the J 41413-SPT.






Customer: replied 6 years ago.
One more question, maybe this will spark that it could be something else as well? When I fill my car while driving out of the station the fuel needle automatically goes down to empty; it will usually go back to normal on about the 3rd time I start the car. It then begins to accurately measure gas amount, however, I think lately it may not be reading it well.....what would this be. I was told it had to do with the light too, but dont remmeber what they recommended needed fixing.

This sounds like a faulty Fuel Level Sensor. This is an extemely common fail item in GM vehicles. GM says it's due to the additives in the fuel pre-maturely wearing out the "teeth" that hit the striker on the sensor. New, updated versions are available. However, when this sensor is faulty, it will not set a P0455, it will set a P0462 or P0463 (commonly)

Customer: replied 6 years ago.
Yes that sounds familiar. I think that was the original diagnostic; this other code I did myself at autozone and I did not know what I was doing. the fuel sensor must work properly to pass emissions, correct. From your experience with malibus, is the only fix replacing the sensor and is that a very costly endeavor? I want to "save" this car because I have never had any other problem, and I have a 16 yrold about to get his license.Thanks for your help

In my State, I am an Inspector- and to be perfectly honest with you... If the fuel gauge does NOT work correctly... SSSHHHHHH!!! Keep that to yourself. If there is NO p-code setting the engine light that SAYS the fuel gauge doesn't work (P0462) then who's to know the wiser?!?! If the code IS present, yes, it will need to be replaced. It's mounted to the side of the fuel pump assembly, located inside the fuel tank. To access it, the fuel tank will need to be removed. The sensor sells for around $150 and the labor time guide is around 2 hours to complete the job.

Customer: replied 6 years ago.
OK thanks - it sounds like to me I should.
1) Buy a better gas cap - that could possibly turn the light off with time, correct? Where can I buy one and could you recommend one?
2) If this does not work or maybe I will still go ahead and "smoke" the system.
3) plug the code system in one more time in a few days to see if the number changes and the other code shows up.
Finally - and these are my last questions, I do appreciate your help. With the present code am I doing damage not addressing the issue immediately? I have till August.
How long do I have access to your answers as I am not near a printer at the moment.

1) Yes. Try a better quality Fuel Cap. Optimally, a GM original, however, I do believe NAPA parts come very close to OEM specs. Ask before you buy. If you believe the fuel cap is good, the light will shut itself off in 50-75 miles of driving. You CAN reset the light yourself by removing the "NEG" cabel from the battery for 15min. HOWEVER! At this point, i wouldn't suggest that until AFTER you have the codes re-read to see what's stored in the memory right now.

2) If it does not work, yes, have it smoked. It's the quickest way I know how to find a leak. Why kill yourself looking for something you may not be able to see. Let the smoke do the work.

3) See (1) above. Yes. Re-read the codes, know "for sure" what you "need" to do.

With ANY EVAP code, no, you are doing no damage what-so-ever. An EVAP code is strictly for emissions and has no bearing on engine performance at all.

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