The power door locks utilize individual solenoids in each of the doors that activate the door lock mechanism. The switch provides power to the door lock solenoids. To lock the doors the switch provides voltage to the two terminals of the solenoid. To unlock the doors the switch reverses the polarity of the voltage applied to the solenoid. An inoperative power door lock can be caused by the switch, solenoid, wiring problem or mechanical problem within the linkage of the affected door.
If all of the door locks are inoperative, start your diagnosis at the fuse box. Inspect the fuse that protects the door lock circuit to ensure it is not blown. Consult the fuse box placard or your owners manual for fuse designations and ratings. Operate each door lock switch in the vehicle to determine if the doors can be locked with any of the switches. If the doors lock with any one switch the most likely problem is a defective switch on the door that is inoperative. If all of the door lock switches are functional but one door fails to operate, the most likely problem is an open circuit in the circuit between the switch and solenoid or a defective solenoid in the affected door. You should listen to the affected door while energizing the door lock. If a click is heard but the lock did not engage, a problem with the door lock mechanism or linkage is the most likely cause.
PRECAUTIONS, TIPS, and NOTES
An inspection of the rubber boot and wiring harness that connects from the door frame and the door can often reveal wiring damage. A volt meter, available at any auto parts store, can be used to check the voltage to the individual lock solenoids and switches. Refer to the meters instruction for proper usage and precautions.