the check engine light or maintenance light , what kind of car? year? If the check engine light comes on its a emission problem that has been sensed by you ECM and I don't think a thermostat would cause your check engine light to illuminate . The first and cheapest and easiest thing to do is to change your gas cap 90% of the time this is the cure. your ECM will reset it self but I think it has to be driven for a couple of hours of constant driving or 200 miles one or the other. But if the gas cap doesn't make it go out you will need to have the fault code down loaded using a code reader you can buy one if you want to do the repairs your self or have a tech. do it and then have him tell you the problem and you can repair the problem or have the tech do it .
Mistake #1 is going to Auto Zone for anything other than purchases in a bottle or can. Take the car to a trusted private mechanic or dealer of the car if you want the car to be repaired correctly the first time.
You really should post the code number to get a good answer and save yourself a lot of work.
My engine light came on. Took it to autozone and went through the whole finding what the problem could be deal. I narrowed it down to it being the thermostat and I changed it myself and the engine light is still on. I know that maybe after driving it around a few times it might come off but I can also unplug the battery and plug it back in. My question is if I unplug it and plug it back in and light goes away, will it come back if the problem is not fixed? Say I bought a faulty thermostat or I was mistaken and the problem was something else.
Thank you
