Service and theft systerm light come on

Chances are the passlock sensor on you 2003 Chevrolet Cavalier is failing. The best way to confirm this is to check fault codes using a scan tool and then properly diagnose any stored codes. The passlock sensor is part of the ignition lock cylinder. It may be a bit tricky for you to replace yourself. For more information on GM passlock system please use the following link - http://repairpal.com/gm-passlock-anti-theft-systems. Here is another link to find a repair shop near you if you decide to go that route - http://repairpal.com/chevrolet-repair-in-sylvania-ohio.

This would be a wiring problem that I explained to another person above. Your anti theft light will come on, as well as the service light with the little yellow wrench underneath? It's a wiring problem. Sell the car. I ended up having to pay a dealership over 500$ in diagnostic fee's and they still couldn't find which wire it was.