check engine light 2002 camry

First thing to do is check to see if gas cap is tight. Loose cap can trigger the light. If it was loose the light should go out after some starting and turning off the engine.

You have asked a very profound question as there could be mutliple reasons. The gas cap is the most simple to check. If that's not it, the ECU code would have to be checked. The dealers can do this but call around to see if there's anyone else that is willing to do it for a cheaper price.