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'02 Impala 3.4L 195.4k: Replace Factory Gas Cap Gasket?

I’ve been getting the gas cap code off and on for years now. I can wash the gasket off and it goes away for a few months, but then it returns. The cap itself is in showroom condition. It’s just the rubber gasket/ring that appears to be “segmented” all the way around.

Has anyone ever replaced just the gasket on the gas cap for this vehicle? I know I can buy a whole new AC Delco gas cap from Rock Auto for $20, but to me that’s wasteful. Looking at the cap, I really can’t see how it comes apart, though. No visible screws, but it must separate somehow … or would you just use a pick and pull the gasket up and off that way?

Sounds to me like the gas cap gasket is rotten

Replace the entire gas cap and be done with it

Either a genuine AC Delco/GM cap or a stant

You can’t get just the gasket. Maybe for some other car manufacturers, but not for GM, AFAIK

I advise you to NOT order from RockAuto

Here’s my reasoning . . . GM has had many, many different gas caps over the years, some of which look very similar, yet won’t seal properly

Just go to your local Chevy dealer and buy the part. Let them look it up for you, based on your VIN. If it’s wrong, you can easily and quickly return it, in exchange for the correct part. If the factory cap has the tether, the cap from the dealer also will. The aftermarket caps will NOT have the tether, if that’s at all important to you. It is to me, FWIW

If you order the wrong part from Rockauto, or if they happen to send the wrong part, it might be somewhat of a hassle and an inconvenience, to exchange it for the correct part

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+1 to db’s post.

Make sure the end of the metal filler tube is shiny clean. If not, even a perfect gasket on the cap won’t seal correctly for long, if at all.

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If you don’t want to get a cap from the dealer ( best plan ) go by Auto Zone and you can make sure it fits while you are there. Why by something like this online, pay shipping and possibly have to send it back with restocking fee and more shipping?

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I buy from Amazon first, rockauto second. Amazon already has fitment check built into their web page and charges nothing extra for exchange if by some miracle it doesn’t fit. If prime member, comes in 2 days with no shipping charge…

I hear your line every day.
’’ but all I need is the . .xxx. ''
They make them is pieces but they don’t SELL those pieces.

buy a gas cap
just clean every so often and don’t forget the neck surface per NYBo.

Had a code, replaced gas cap with one bought from the dealer, Had a key not working consistently, no chip dealer cut a few new ones based on vin and worked fine, did front and rear differential, dealer had fluid with anti slip whatever already included vs, here buy this, then add this, can’t even get a cig lighter that works except from the dealer, my moral of the story, sometimes it is better to go to the dealer for parts, though thermostat and starter motor were NAPA brand, air and gas filter whatever brand, though with the gas filter it connected fine, but was larger than oem and would not fit in clamp shut plastic housing and zip tied it in place.

Moral of the story, mixed bag.

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When my Corolla’s gas cap fails to seal I rub a little engine oil on it, just a tiny amount, enough to barely coat it. That has always worked for me, and the cap is original to the car, over 20 years old. The rubber seal is fully intact though. If your seal is actually broken into segments – and assuming it isn’t made like that – then your best bet is a new oem cap.

I should add that I had a problem on my 40+ year old truck earlier this summer of a similar nature. I thought that a neighborhood kid might have been playing a prank on me and putting something in my gas tank. I continue to think that in fact did happen. I have locking gas caps, but one of them has never really locked correctly. So I decided to fix it, and removing the seal was part of the process. Unfortunately the seal broke, leaving me with a cap that would lock, but no seal. Every try to buy a replacement for a 40 year old gas cap seal? … lol … What I ended up doing was make my own seal using some RTV caulking material. Seems to be working w/no degradation so far at least. An imperfect solution, but better than nothing. That’s my objective !!

OK, maybe I misled you guys. The cap is in showroom condition and the gasket is fully intact. By “segmented” I meant when you look at it, it appears to have spiraled lines - like a candy cane - all the way around.

But maybe that’s normal … I don’t know. I’ve never really looked at it closely until I started getting the code.

And in addition to wiping the gasket, I’ve wiped down into the filler neck and all around the outer sealing edges too. It’s clean as a whistle. Lasts for a while, then the code returns.

Just looked on GMPartsDirect and the GM part number is #10372867

Alternate number is “GT279” (which is ACDelco)

The depictions of both caps are identical, and both show the tether, but maybe you cannot trust the pictures?

RockAuto, has the ACDelco cap for $19.70, while the GM cap is currently out of stock.

Amazon has both with the ACDelco cap around $20 and the GM cap around $25.

Ridiculous that you cannot replace a lousy gasket on these caps. Not even sure the problem IS the cap. Just guessing here. Maybe I’ll try Vaseline or oil to try to prove it’s the cap …

It’s time for a smoke test of the evaporative emissions system.

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Another possibility, and I’ve seen this numerous times . . .

the evap purge valve can’t pull a sufficient vacuum


Probably just buy the cap and try that before paying for a smoke test. Looked into making my own smoker earlier this year for testing my '97 Taurus engine. Too bad it’s all apart right now or I’d just use that as my smoke machine (LOL!). Maybe need to revisit those home-made smoker ideas on YouTube…


Wouldn’t I get a more specific code if the purge valve was the problem? Maybe not, right?

Not necessarily

Why don’t you post the EXACT code you’re getting, please


P0442 : EVAP Very Small Leak Detected

No gas smell, and no drivability issues. Most likely the cap.

Just read and cleared the code again (@ 195,606 miles). Gonna track how long it takes for it to come back. Then I’ll try the Vaseline or oil trick to see what effect, if any, that has. If it does have an effect, that would indicate a gasket losing pliability?

Let me ask you this: over the years, when I clean the car twice per year, I’ve noticed more “soot” buildup all over the white paint - including inside the gas filling alcove (which is odd because that area is covered by the filling door). Is this an indication of fume leakage inside the fuel filling alcove (it’s really sooty in there)? Or is all this “soot” just in the air (or coming from the car’s exhaust) and it’s sticking to my paint because I’ve always wiped the car down with Formula 409 and paper towels. When I wipe the car down it looks showroom new, but this “soot” is everywhere - including inside the door jambs. Makes me wonder what kind of air I’m breathing down here on the Southeast coast …

[quote=“ColtHero, post:15, topic:96239”]
P0442 : EVAP Very Small Leak Detected[/quote]

That code is quite vague. You are right it could be the fuel cap, or it could be any of the connections in the diagram below, or even purge lines in the engine compartment if here are any.

Was driving home from work in the dark and clearly saw the CEL come on at 196,007 miles - so 400 miles later. Same P0442 again, so I cleaned the gasket, coated with a little petroleum jelly, and cleared the code again. Now we’ll see what effect, if any, this has.

I wish I had gotten into this conversation a little sooner. I would have recommended that you use a little silicone grease from one of those little packets you get for spark plug boots instead of Vaseline.

The soot around the gas door is a mold that is peculular to hydrocarbons. So that is an indication that you have a small leak from the gas cap. But the leak may not be from the cap to tank seal, there are other internal seals in the cap.

I see a new cap in your future.

Hi Keith!

Yeah … I should’ve thought about the silicone option. I didn’t really want to use the petroleum jelly because I was concerned it might dry up and flake off into the tank, but I made sure to spread it pretty thin so it shouldn’t be a problem. Besides that, probably not the best thing to condition the gasket with (LOL!).

But we’ll see if it has any effect. This is just a little experiment. Pretty sure (at least hopeful) it’s only a new cap that I need.

Hey - still got that Saturn?

fwiw, I’ve always wiped a little 10w-30 motor oil on the gas cap gasket to make it seal air tight so to pass the Calif emissions test required every 2 years for the gas cap. Been doing this for years. Always passes the test, and the oil hasn’t ever damaged the o-ring gasket.