Tighten fuel cap

I have a 2004 Chev Avalanche. Several times recently my check engine light comes on, the truck dings 3 times at me and a dash script tells me to tighten my fuel cap. I do and the light goes out within a few hours or the next day. I have changed fuel caps twice. This week the light came on, has not gone off and at least 3 time it has told me to tighten the fuel cap which I have done. Any idea what is going on?

You clearly have an evaporative emissions leak code

Presuming you bought the correct cap and tightened it correctly, we can assume the cap is not the problem

My advice is to bring the car to a reputable shop and pay for a diagnosis and repair

Might be something as simple as a bad evap purge valve or a rotten fuel filler hose

Try a cap from the dealer.

Remove the gas cap.

Take some petroleum jelly, and apply it to the O-ring seal on the gas cap and reinstall the gas cap.

If this causes the Check Engine light to turn off, one of two things is happening. Either there’s a small leak somewhere else in the EVAP system, or the plastic filler neck where the gas cap screws on is starting to crack.


I used the same tip that Tester is talking about on one of my uncle’s vehicles. It turned out to be a bad gas cap seal. A new gas cap fixed the problem.

Try REPLACING the gas cap

“It turned out to be a bad gas cap seal. A new gas cap fixed the problem.”
“Try REPLACING the gas cap”

Manager Says, "I have changed fuel caps twice."

@db4690 called it. The problem with the “tighten fuel cap” message is that the people who designed the warning message decided (correctly) that when the computer notices pressure problems in the evap system, the most likely cause is a bad gas cap. A high percentage of the time, the problem will be fixed by replacing the gas cap. However, there can be other causes as well. I, too, would suspect the purge valve first.