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Ok, did you replace the gas cap because the fault code retreived using a diagnostic scan tool showed an evaporative emissions leak, or just because you either read it would solve the problem of the check engine light being on or because you were guessing at the possible issue?
Ok, the check engine light only comes on when the onboard computer detects a fault in either the engine management system, transmission, or emission control system. Faults can range from vacuum leak, engine misfire, transmission problem, emission control leak, one of dozens of engine or transmission sensors, or even internal engine or transmission failure. There are over 500 fault codes that can cause the check engine light to come on. And not every one has symptoms you can feel or see or hear.The only way to determine which of the over 500 faults is responsible is to have the onboard computer read with a diagnostic scanner. once this is done and the fault code retreived then pinpoint diagnosis can be done and repair done.without knowing which of the over 500 faults is responsible, it is simply impossible, as well as irresponsible for anyone to guess at to which one is responsible for the check light coming on, and as you found out, guessing doesnt work and causes you to spend money replacing a part that is actually good as you did with the fuel capUnless you live in California, you can run your car by any major parts store and they will retreive the fault code and definition for you for FREE. At that point, you can decide if this is something you can repair yourself or have a professional do the repair
Sorry that I cannot guess as to which of over 500 fault codes is responsible!!!! Or would you rather waste money replacing parts that likely will not fix the problem by doing guesswork.