There are about 20 things that turn the light on. Take it to auto zone and have the codes read for free.Answerthe cause of this could be dew to the smog control, located at the top of the engine around the carbarator area... Answeranother thing could be a broken speed odomitor cable. Answerpull the fuse cover, grab a spare fuse, make sure you don't use a fuse that's being used somewhere else. There is a raised fuse slot at the rear of the fuse box, this is the diagnostic switch. insert the spare fuse. insert the key and turn ignition to the 'run' position when the dash lights come on the 'check engine' light will blink the code out in a pattern. It may blink out several codes, so be sure to have pen & paper handy. the pattern repeates, so don't worry about missing any codes.
12 normal 13 O2 sensor (no voltage or voltage doesnt change) 14 coolant sensor circuit high voltage (low temp) 15 coolant sensor circuit low voltage (High temp) 21 throttle switch circuit (manual transmission only) 21 throttle position sensor circuit (high voltage input) 22 throttle position sensor circuit (low voltage input) 23 MAT/IAT sensor circuit 24 speed sensor circuit 25 MAT/IAT sensor circuit 31 MAP sensor circuit 32 MAP sensor circuit 41 ignition sensor circuit (no signal) 42 crank or cam signal sensor (no signal for two seconds) 46 idle speed control motor circuit 51 EGR system circuit
you can clear the codes by pulling and replacing the 'tail light' fuse. don't forget to remove the spare fuse from the diagnostic slot when you are done. Always clear codes after you do work like replace defective part to see if the code (or another) shows up. There is no way to know how old a code is so just best to clear them. If you didnt fix the problem the code will show up again :)