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'check engine' light is on

recently the ‘check engine’ light went on in my 2005 Chevy Cavalier. since I couldn’t afford the typical diagnosis charge, I went somewhere where they code it at no cost. They said it was the gas cap, so I went to a dealer & bought one. (They also turned the light off for me.) Problem is now the light is back on. While I was at the dealer, the mechanic said it will have to be properly checked to pass inspection; apparently it has something to do w/ emissions. Is that true? Can you recommend a mechanic who doesn’t charge exorbitant prices? I’m on a limited income. Thank you.

It would be helpful if you posted the exact code that was discovered when you had the system scanned. Only by knowing that can anyone be specific with a cure.

However, I will speculate a bit. The “it has something to do with emissions” leads me to believe that the reference was likely to evaporative emissions–the kind that emanate from your gas tank. A loose or bad gas cap can have something to do with this, but it can also be the result of a carbon canister that needs to be replaced, or it can be the result of a bad purge valve in the evap system, or it can have to do with a problem in the lines (hoses) of the evap system.

For starters, if you are one of those folks who continues to do the “click-click-click” routine with the gas pump in order to force more gas into the tank after the pump shuts off at the station, be aware that this is the primary cause of these problems. Stopping this routine might help, but if the carbon canister is totally saturated with gasoline by this overfilling technique then the only solution is to replace that expensive component.

Can I recommend a mechanic who doesn’t charge exhorbitant prices?
Yes, but he is not really competent.

If you want any specific mechanic recommendations, you might want to reveal where you are located.
The members of this forum come from all 50 states of the US, plus a few foreign countries, and getting a recommendation for a mechanic in Mexico might not be very helpful if you live in Minnesota.

Knowing the municipality where you live would be necessary in order for anyone to recommend a specific mechanic. However, if you go to the “Mechanics Files” section of this site, you can do a search based on your zip code. Go to in order to see the Mechanics Files.

It Sounds Like You Had A Code For A Large (Or Small) EVAP System Leak And The Easiest / Cheapest Attempt At A Remedy Was Trying A New Gas Cap. These EVAP Codes Are Among The Most Frequent Causes For “Check Engine” Illumination.

Sometimes a cap will solve it and sometimes the leak can be quite a complicated issue involving the EVAP system, requiring professional diagnosis.

Try something else before giving up. Remove the cap and thorougly clean the gas filler neck where the seal on the gas cap contacts it. It must be smooth when you run your fingertip over it. Don’t make any sparks, duh. To help get a seal and protect the neck, spray the neck with WD-40 and also spray some on the cap’s seal.

I had both large (code PO455) and small (code PO442) EVAP leaks that I fixed this way without even replacing the cap.

Of course you’ll have to get the light turned out again (ask what the code was) unless you have some patience. If you’ve fixed it the light will turn itself off after using the car for several trips. You can also invest $50 and buy a code reader like an Actron Pocket Scan and read your own codes and turn off your own light.

Good luck. Let us know what happens.