I recently asked a question (yesterday) regarding my car which had a check engine light that came on and I had the code read at autozone. It came back as P0126 thermostat malfunction. I got a ton of great information on the problem in the response I received, but I have an update on my car as of today and want some more feedback. The check engine light was on, I was still driving it and put gas in the vehicle to full this morning the 2nd. When I turned my car on after filling up, the check engine light was no longer on. The car has run fine since I got the error code (doesn't take longer to heat up, no rise in temperature gauge passed half way point of H and C, and no other noticeable issues). I am wondering what I should think of this and why the check engine light may have gone away even though I didn't erase the code.
My car has an automatic transmission.
It is quite possible the code was set as an intermittent problem. The thermostat may have been stuck at one point, freed up and began working again, and then allowed the light to go off. Most computer controlled engine systems will allow for a trouble code to either go away after seeing a set number of ignition cycles without the issue, or it may turn the light off and keep the trouble code stored in memory. In either instance, I would view this as a sign that there is a possibility that the issue will come back. I would have the codes scanned again to see if the code is still present, and if it is not, I would just keep an eye out for it to reappear. If you feel you need a hand with diagnosing/repairing the issue, contact a certified mechanic, like the mobile mechanics available at YourMechanic.com.