ETS OFF + Check Engine light

I have a 1996 Chevy Cavalier (2.2L - 4cyl) and the other day my "ETS OFF" and "Check Engine" lights came on at the same time. We stopped, checked the car over, the only visual problem we found was that the gas cap was not on tight. We tightened it, filled up with gas and drove around. But after a few short driving trips the light is still on. Any ideas? The car runs fine but that pesky light just doesn't want to go off. Are these 2 lights indicating the same problem or 2 separate issues? Could it be serious?

vacum leak

You could always run down to your local car part store and have them read the code. Many stores do this for free these days. Otherwise anything is just a guess as to what is wrong.

Unhook your battery for a couple of minutes and the lights will go out. If they come back on later on then you know it's not your gas cap.

I had the same problem with my Cavy. It was the TPS (Throttle Positioning Sensor) When mine went, the gear shifting was also off which caused a clunk when shifting gears and jolting until the problem was fixed.