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Gas cap issue

2007 Suzuki XL 7 110.5K miles. Check engine light came on with message on display “tighten gas cap”. Went to auto parts store where they did a scan and verified this was the issue. Replaced original gas cap with after market cap and allowed sufficient time for codes to clear. Check engine light never went off and message popped on occasion.

Exchanged cap at same store. Check engine light still on with occasional message.

Should I be looking for an air leak in the fill tube or go with OEM gas cap figuring that the after market cap is poor design?

Apply a small amount of petroleum jelly on the gas cap and on the filler neck and install the gas cap.

If the code returns, the small leak is elsewhere in the EVAP system.


Not to be snarky . . .

this is the exact reason why paying for diagnosis is very often worthwhile

Just because a code or message says “tighten gas cap” doesn’t mean the gas cap is automatically the problem

This is where the pro comes in to diagnose and repair the problem, in a systematic and logical fashion. And he will also verify the repair. Verifying the repair is FAR more than clearing the code, driving around the block and calling it good

If the gas cap is missing or has a clearly torn seal, it’s likely that was the cause

But it sounds as if that may not have been the case

A shop will use a “smoke test” to try to find the leak. It’s basically a smoke machine that pumps smoke into the evaporative emissions (the hydrocarbon-saturated air in the gas tank and its peripheral places). The smoke comes out where the leak is. It’s a cost-effective way of diagnosing an EVAP system leak.

However . . .

Just because the smoke machine finds a leak, do NOT assume the leak was the only problem

There are a few cars out there with one fault code, but multiple problems

Again, this is where verifying the repair comes in

After fixing the leak, you verify the repair. And it is at that time you might find it has more problems. And you realize you’re not quite done yet.

For example . . . the smoke machine finds the rotten gas cap, you clear the code and send the car on its way. But the purge valve can’t pull a vacuum, or the hose connecting the valve to the manifold is no good, or fell off. Soon enough, the car will have 2 consecutive failures, and the MIL we be on again

That’s where running the evap service bay test comes in. If your scanner is incapable of initiating the evap service bay test on a specific vehicle, at least drive the car under the appropriate conditions, so that the evap monitors run to completion

Or you could disregard what I said and take your chances

More often that not, you’ll probably “get away with it”

But that one guy might be upset and rightfully so. And he might tell plenty of people that your shop is lousy, as far as diagnosis and repairs are concerned. Might hurt your business :frowning2:

Agreed. The smoke test is only a place to start. It isn’t perfect, and it isn’t necessarily the end of the work to be done. But at some point one needs to stop changing the gas cap repeatedly hoping for a different result. :pensive:

But then we wouldn’t need this forum. Most question deal with diagnosing a problem. All the drunks here, unemployed, retirees and PC forum fanatics wouldn’t have anything to do but go back to a normal life.

“All the drunks here . . .”

Don’t know who you might be referring to



You’re right, Kurt. If it weren’t for this forum and women I wouldn’t have much reason to get up in the morning! :grin:

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For me,the drunks on this forum have been more helpful than the mechanics I use. I think I have to take a breathalyzer with me next time.

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