I have a 97 Grand Prix GTP and the "service engine soon" light recently came on. My last fill up was with unleaded gasoline but you're supposed to put premium in the GTP. Would this be why the sevice engine light came on? BTW I filled up on saturday and the light came on monday.

 

Nevermind, I took it to Autozone and it turns out there was a misfire in one of my cylinders. Most likely caused by a bad plug, I'm gonna check it out tomorrow.

 

misfires are usualy a sign of running lean. Like an air leak/vacuum leak or faulty injector. Don't discount them.

 

premium is unleaded fuel. all fuel unless you have a race or maybe an aircraft pump is unleaded. so are you saying that you put in regular, as in 87 octane? if so that can cause your check engine light. did it come on under a high rpm? or when it was really hot out/engine really hot? is this the first time you used regular instead of premium? when a manufacturer says to use premium fuel only, its because a low grade is proned to knock in a high compression/boosted engine. knock is a missfire, and can set a code like yours. buy a few of those sts or whatever brand of octane booster from a parts store or gas station. and rais your octane up to 91. if you still have a problem, then suspect plugs or vacuum leak..