Code just came up and have been reading the threads.

When I went to check the cap tightness and seal, I noticed a significant amount of back pressure when I opened the cap. Not normal for my car.

Could this have caused the code and if so, where should I be looking?

 

I suggest you look at the purge valve under the hood, it should be closed and you should not be able to blow air through it.

https://www.obd-codes.com/p0442

Then there’s the under the car EVAP valve, check it for leaks

have a look at the fuel and vapour lines under the car, any corrosion at the bracket clips? Can you smell fuel by the driver’s rear tire?

Year , model, mileage, any recent repairs done?
All clues to curing that P0442

 

Year, 08, approx 156k, no repairs or mods. Just came on out of the blue. No smell of gas. Have not gone under car yet.

Started off simple steps first.

Looked for rust around filler nozzle. Slight hump of light rust around edge. Not sure it would effect seal. Sanded off.

Looked closely at cap seal. No cuts, cracks or dry rot. Was quite dirty so cleaned it with rag and WD40. Nice and clean.

Removed fuse from battery terminal to clear the code.

Code is gone.

Went for a quick drive and parked. Cycled the engine on and off a few times. No code.

Will report back either way to follow up.

 

Possibly it was the cap or the filler neck surface, I will take a moment to advise , if you do order a new fuel cap, don’t go cheap, get an AC Delco for your year, I ordered an AC Delco cap from Amazon, it was a counterfeit part from China, it did not work. I ordered an AC Delco from RockAuto and that part worked and cured my issues.
Just stating a fact of what I experienced.

Please keep us posted about this. Thanks

 

Did anyone fuel up while engine was running? It'll set that code. It'll eventually clear and turn out the light.

 

Hope you nailed it but if not fixed it still takes quite awhile for this code to come back. I have struggled with this for well over a year. It takes up three weeks for mine to come back and set CEL. The codes shows up pending well before that.

I have not eliminated ALL causes but was lucky enough to talk to an actual GM fuel system expert. There are SO many possible causes. May even need to replace the fuel pump module.

There are several other threads on this including the "related thread" I found following this one. (They probably change.) It was https://www.chevyhhr.net/forums/prob...e-p0442-64965/

 

One of the most common causes is a leak in the vapor tube in front of the driver side rear wheel. The tube next to the fuel tube. They often rust out under the clamp.
One of the less common causes is one or more of the seals on the top of the fuel tank is leaking.

I'm not sure what you mean by "back pressure"? Hard to pull the cap off? Makes a hiss when removing cap? feel air going in or out when removing the cap, which one? In other words, suction or over pressure. While engine running, after it has been shut down for several minutes etc?

 

Suction or over pressure. Good question. I assumed it was over pressure because it sounded like it was blowing off. But now I will have to pay more attention.

Checked after driving and shut off after driving home. So, hot car.

To update, the code has not come back yet. No fuel smells or anything unusual.

Advice taken on AC Delco cap.

On the fuelling up while car running. I have done it many times without setting off codes.

 

NEVER fill up with engine running. Besides being dangerous and illegal is some places the computer depends on the engine being off when data is collected.

 

Can you elaborate please?