I just had a tune up at pep boys a week ago and now my check engine light is on. I had a diagnostic test when I got the tune up, and it cost me $89 for the test. I've heard that Autozone and Napa Auto do free diagnostic tests, only this service is not available in CA for auto zone, and I'm trying to research local Napas now. I don't want to go back to pep boys, I have a little bit of a beef with them from last time. Does anyone know of any place in the san fernando valley that offers free engine diagnostic test?