I have a 2004 Impala LS that has the door lock actuator with anti theft sensor. The door lock by remote and buttons in car always worked fine. When I was in parking lot backing up another driver cutting diagonal across the rows tapped my rear bumper at an angle on driver side corner. The contact set off my anti theft alarm and stopped the engine, locked the doors, and horn and lights flashing. I tried open the door with it locked then pushed the door lock button, then finally used the manual **** to open my door. Ever since that my driver side actuator quit working, all the other doors work by remote and switch except driver door. I thought maybe the actuator motor died in that and changed actuators and still my driver door will not work by remote or button. The actuator I put in does work I tested the motor with 9v battery. So I decided to take my old original actuator apart to look at the electric motor. The electric motor was burned up with huge spot of rusty looking discoloration and also the copper contact prongs coming out of electric motor were also completely discolored with this grey / blue looking color. I sanded down the contact to the copper so the discoloration is on the outside.

Any suggestions on what to try next to diagnose?

No, nothing is modified on the car. Yes, the car was running and moving in reverse when contact tripped the car alarm and yes the anti theft cut the engine off while I was moving in reverse. Yes all switches and fob remotes lock and unlock all the other doors except only the driver door.