Evaporative Emission System Leak

2009 Impala, 50000 miles, runs good, however service engine light is on with a DTC showing P0455, “Evaporative Emission System Leak Detected, Gross Leak/No Flow”. Are there obvious things I should search out or has there been a common problem in the EVAP system on this make and model that would help me to pinpoint the leak?

Are you sure the fuel cap is on, or maybe on but loose? That would be the first thing to check.

The evap system is what allows air into the top of the gas tank as you use up gas as you drive. If it didn’t, the car would quickly come to a stop as the vacuum would prevent fuel flow to the engine. If the car is running fine, that part must be working ok. It’s a tricky business, as it has to allow air in top fill the void of the used gas, but not allow gasoline fumes to vent out. It’s probably this second function that is causing the CEL. The car’s computer (ECM) tests the evap system periodically to make sure no fumes can escape, and in your car the ECM is saying there is a way for fumes to escape. It could be something else, but it might just be the gas cap.

Thanks for the response. I just checked the fuel cap, it appears to be on properly. If at one time or another it was not put on securely would this set and hold the code and then I would have to clear it to see if the problem is solved?

If the cap was off or loose earlier, the ECM might have found the leak then, and set the code. If so, and now the cap it on ok, the ECM won’t turn the CEL off until next time it does the evap test. When it does it varies car to car. Many cars do it on a transition at the 1/4 full or 3/4 full mark. Maybe fill the tank, then drive it past the 3/4 full mark. Might work. Best of luck.


Keep the purge valve in mind as a possible culprit

If it intermittently sticks open, you’ll get a gross leak code

Not that uncommon on GM vehicles

Thanks…I think I will start there


It’s $14.40 at rockauto.com

You should be able to easily replace this yourself.


Thanks! I just finished ordering the part as you directed. It would have cost me nearly double that at NAPA


Lets us know how you make out.

Only time will tell if this was the ultimate solution . . .

I installed the new purge valve under the hood (simple job), started the car a dozen times within a few minutes but the service engine light remains on. Do I need to take the car somewhere (AutoZone) to have the code cleared and then see if it comes back, indicating problem is not corrected?
Also I was informed that there is a similar part back by the gas tank that may be the problem…true? Thanks!


If the purge valve was your problem, the pcm will eventually extinguish the light on its own

The other part back by the gas tank is the evap vent valve

Thanks…I’ll wait a few days of driving and see if the code clears itself. I checked Rock Auto parts but could not find the evap vent valve…our local NAPA wants $68 plus tax for it.

Alright!! the code for the EVAC clear itself yesterday…the check engine light is off, so the new EVAC purge valve solved the problem! Thank you all!

Crystal_Clear, The EVAP Vent Valve/Solenoid That Probably Needs Replacing (Fairly Common Warranty Repair On The 09 Impala) Is Located Back By The Fuel Fill/Fuel Tank Area.

I believe the part is 25932568 (I believe it is revised). Failure of this part can result in a Check Engine Light and code PO455 (large EVAP leak) will be found.

Don’t do anything else until you call a Chevy dealer and see if it’s possible that if it is indeed this particular problem it would be covered by warranty. Some emissions items are covered by a longer warranty than that included in the 36month/36,000 mile bumper-to-bumper warranty.

An experienced service person at a dealer will be quite familiar with this. Most dealers stock this item.

The part is not super expensive and warranty labor only pays a mechanic .6 hour to install.

I Reread Everything.

You could clear the code and see if it comes back, but if you go to a dealer for a warranty fix then you’d probably be better off leaving it alone. See what your friendly neighborhood dealer has for advice.


I do not know if your car works this way, we had a Dodge van with a similar problem. There was a pump to pressurize the system for the check, the pump failed thus an error code. New pump and all was good.

@crystalclear, congrats on getting your evap problem fixed. Other things can cause evap problems, but purge valve failures are pretty common complaint here. Not exaclty sure why, it would seem a purge valve could be designed to be close to 100% reliable. There are a lot of gadgets way more complicated on a car than a purge valve. Maybe somebody here knows what it is that is causing all the purge valve failures.

One thing that may help going forward. The experts here recommend to not overfill the gas tank, as overfilling can damage evap components. When the gas pump clicks, best not to top off.

I wouldn’t exactly say that there’s an epidemic of purge valve failures.

In fact, I’d consider them fairly reliable. By they time they fail, the vehicle is usually several years old. And the replacement will usually also last several years.

Likewise, if an oxygen sensor heater circuit failed after 10 years, I also wouldn’t consider that a problem or design flaw.

Thanks everyone for all the comments. All is well…the check engine light went off by itself and has not returned…I assume the purge valve was at fault. I will admit that I have a habit of topping off the tank to the max and then some. I’ll refrain from doing that anymore. If this code, P0455, appears again I’ll check with the dealer first.

You can reset the CEL by disconnecting the battery for a minute or two…

It is very seldom that air must be admitted to a fuel tank to replace the fuel as it’s burned…Gasoline has a natural vapor pressure of 4-8 PSI which keeps the tank pressurized even as fuel is being consumed…The EVAP system’s job is to collect these vapors and feed them back into the engine instead of letting them escape into the air…If replacing the purge valve doesn’t solve your problem, the diagnostic tool used to find EVAP leaks is a “Smoke Test”, where they blow a chemical smoke into the fuel filler and watch for where it’s escaping…