Check engine light

Our 1997 Blazer has the check engine light on. We've checked and topped up all obvious fluid levels, engine runs great, no transmission shifting issues, back brakes need to be bled I think. Just did an oil change and put in a air filter (the previous owner didn't have one in for some reason...not sure how long it ran without it).

Any ideas on what may be causing this?

check out the o2 sensors if not take it to advanced auto parts and they will hook up a computer to tell you what is wrong check engine light can be anything even your exaust

The very first thing you need to do is get the codes and post them back here

Was the light on before the air filter change?

youre better off going to AZ than advance ;-D

however, you do need to get those fault codes.