2001 jimmy,runs really good,sometimes idles a little rough,any ideas on why the light is now out?,,i wouldnt be concerned about this but i need to go thru emissions in oct or nov.,,maybe it needs a ?,crank sensor relearn,is that just a computer thing ,like reprograming the computer?,,thanks for your thoughts

 

Did the check engine light stay "ON" while running, or did it always go "OFF" after starting the engine?

 

it was on then off then came on again,now its back on for good?

 

If it happened over a long period could be the gas cap wasn't on tight and that turned on the light, then you tightened it. Then not tight again....
Could also be someone erased the code and that turned off the light, for a while. But the issue remained and after the next driving cycle it came back on.