check engine light on 2004 Toyota Corolla

Check light just came on stays on but soesn't drive different. What is involved in servicing and about how expensive to fix. I bought extended warrenty with car 5 month ago.

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1 answer 1 comment
The check engine light is an indicative that the vehicle's computer has detected a failure on the emission controls system. You will need to retrieve the trouble codes to diagnose the problem. Learn more about it here; http://repairpal.com/check-engine-light
If you fail to tighten the gas cap to a certain point the CHECK ENGINE light will come on.