I have a 2001 Chevrolet Cavalier with a service engine soon light on constantly.  You  can reset the computer and it will go off until you put the car in gear. Then it will cause  the DLR light to blink and the left headlamp will blink repeatedly for several seconds the  go off but the service light then comes back on. Any ideas?

JK: Sounds like you may have a wiring problem to that headlight. This would also cause the Service Vehicle light to come on.
A common problem on the Cavalier is green / corroded wires in the harness between  the left and right side headlights.

You will need to take apart the harness and tug on the wires looking for one or two to  break.
2002 chevy cavalier old battery removed and replaced with new one.
Question = my mother is the second owner of a 2002 chevy Cavalier. I replaced the battery and now the Theftlock for the radio is on. I would have asked the first owner but he's dead. So was wounder if you have the
radio codes and how to put them in.

Newer model vehicles do not use a security code that can be entered in like older model vehicles. The radio must receive the vehicles VIN from the serial data line of the vehicle The radio should not be locked after a battery disconnect. The only way to unlock the radio is with a class 2 scanner.
Chevrolet Cavalier Headlight And Radio Problems

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