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I'm trying to figure out why the power lock is not working in one of the doors of a 2004 Buick Rendezvous, unfortunately I don't really understand how the power lock system works. There are two connectors attached to the lock mechanism, one near the top and one lower down. The connector near the top has three thin wires, red, black and blue with white stripe. The lower connector has two thicker wires, olive (greenish) and tan (brownish).

When the lock/unlock buttons are pressed, I can measure continuity between the blue with white stripe wire and ground (chassis). No other wires seem to be connected to ground, or each other no matter the state of the lock/unlock switch.

I'd like to determine if the problem is with the actuator or the wiring, before I just start throwing money at the problem.

I have not been able to find any schematics online, nor was I able to locate the Haynes repair manual for this vehicle. I'm basically working in the dark on this, and would appreciate any assistance I can get.

Additional information:
According to the installation manual for the remote start module (installed before I owned the vehicle), lock works via a negative trigger through a 470 ohm resistor, while unlock is a negative trigger.

The lock/unlock feature of the remote start is not hooked up, so I don't suspect that could have caused the failure.

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2 Answers 2

Reset to default
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The power door lock circuit includes the Body Control Module, Door Lock Switches, and Door Lock Actuators.

The upper plug has no relevance in the circuit and is used partly as the door ajar circuit.

The lower plug with the tan and gray wires are for the door lock actuator.

The door lock switches are 3 wire. Black is ground, red/black is output signal to the BCM and gray is for the switch light.

The BCM provides constant power on both wires to the lock actuator and will ground one wire or the other to lock or unlock the latch.

If you don't have power on either lock actuator wire.

  • Inspect the harness where it feeds through the rubber boot into the car body.
  • At the BCM backprobe pins 1 & 2 on the A connector, pins 1 & 2 on the B connector and pin 1 on the C connector for power.

If you don't see ground on the lock actuator wires while pressing a switch.

  • Check the switch for ground on the black wire.
  • Check for switch output on the red/black wire.
  • At the BCM backprobe pin 4 on the B connector for ground while pressing a switch.
  • At the BCM backprobe pins 1 & 2 on the A connector, pins 1 & 2 on the B connector and pin 1 on the C connector for ground while pressing a lock switch.

If the ground from the switch to the BCM is ok and the BCM doesn't ground the lock actuator pins replace the BCM.

If all wiring & BCM output is OK replace the lock actuator.

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Check the manual for resetting the locks. There is 4-5 different options. I had same problem and was able to fix it by reprogramming on dash board.

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