Then use your test light or digital meter to check for power and ground at the connector when you operate the lock unlock switch.
Gm power door lock troubleshooting.
If all of the door locks are inoperative start your diagnosis at the fuse box.
If the power door lock relay fails it will cut off power to the entire power door lock system and may cause them to not function correctly.
For vehicles equipped with door lock cylinders the door can still be opened using the key.
An inoperative power door lock can be caused by the switch solenoid wiring problem or mechanical problem within the linkage of the affected door.
You should see the voltage polarity toggle with each switch activation.
However vehicles without door lock cylinders will not be able to lock or unlock the doors until power is restored.
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Inspect the fuse that protects the door lock circuit to ensure it is not blown.
Power door locks that do not function are another common symptom for a problem with the door lock relay.