Engine Light on 2003 Pontiac Vibe

My "Check Engine" light just came on. My Vibe has 172k miles. Just bought from a dealer "As is". They did warn me about this coming on due to possible catalitic converter problems that was a common issue with the Vibe. Is there anything I can do 1st to check before going to a mechanic. I like the gas cover being replace idea. Will do that. Please advise. Thanks.

Asked by for the 2003 Pontiac Vibe
The check engine light can come on for many reasons, hundreds as a matter of fact. Sounds like this dealer knows that it had a problem when they sold it you, but I would still have it looked at before jumping to any conclusions. The first step is to retrieve the diagnostic codes in the engine control module, then look to see what the codes mean. You can do that here:
Thanks, but how do I look for the engine control module?
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my check engine light came on also turns out it was the gas cap make sure it is on right or replace it. cheap fix if thats the problem. I did not need a new one I just didnt have mine on all the way . It took a few miles but then my check engine light went off. has not come on at all. just a thought