On my Grand Am, I had a problem with the maintenance soon light constantly on. I went to the Sears auto shop on Grand Canyon Drive. They did their electronic check and found nothing. However they did say that in most cases, it's a bad gas cap. So, I go down to the local Auto Zone buy/install a new gas cap. Good news, problem fixed. Bad news, none. Sears charged me $0. I went early so there was minimal wait time.