this can be caused by numerous reasons like mine been on because the mass air flow blew out from my cai, then my spark plugs burnt out and killed my coil, also if the ride hieght is not level while you start the car it can throw it off, burnt fuses, im sure the list just goes on and on but really the only way to really find out is by scanning the car and getting the code!
Mine was a censor that was out. I can't remember which, but if I have a chance tonight I'll run to the box and check my receipts. It cost me $100 as I have a 100 deductible. But otherwise it would have been $140 after installation from Toy dealer.