Why does SES light up without engine running?

I have a 1999 3.5 with 92k miles.

My SES light goes on and stays on when the igniton is in the start position (the other dash lights go on briefly then go out) but before the engine turns over. It then remains on while running.

Any thoughts on what may cause this before I get codes read?

P.S. I recently cleaned my MAF sensor. Looked fine.

Could be practically anything. Was the light on before you cleaned the MAF sensor? Did you plug the MAF sensor back in?

I dont know where youre getting the codes read at, but please dont pay for it. Most auto parts stores will read the codes for free. Just jot down the codes and come on back here.

Better yet, get on Ebay and snag yourself a cheap OBD II code reader, I think I paid like 25 bucks for mine and its been a godsend. Its nice to be able to read AND clear your own codes without having to stop somewhere all the time...especially since most auto parts stores wont clear it for you, just read it.