2000 Cadillac STS, Door Locks Cycle Up & Down While Driving

This 2000 Cadillac STS came in with the complaint that the power door locks would not work from the driver’s power door lock switch  and that the door locks would cycle up and down while driving down the road. All other functions on the driver’s door worked fine. It took me a little while to go through this system and develop some test procedures. Now that I know what to look for it should only take a few minutes to do the basic tests. First the power window switch mus be removed so that circuits can be tested on the underside of the switch. push in on the spring clip and lift the switch from the door panel.

Using a volt meter check the voltage on the red/black wire, terminal #7 and the orange/black wire, terminal #6. There should be a nominal 5 volt signal present on both wires with all switches in the rest position.

The voltage on both wires on this vehicle varied between .5 and 3 volts with all switches at rest. Dropping down below roughly 2 volts can trigger the locks to cycle.

Now I need to disconnect the power door lock switch and that requires removing the door panel. There is a Phillip’s headed screw in the lower left corner of the panel.

The cover behind the inside door handle has to be removed. It takes a gentle touch and even then one of the clips will likely break.

Now, a Phillip’s head screw is revealed for removal. A #3 Phillip’s screw driver works best.

The flap behind the inside door pull handle is held down with Velcro tape and takes a little effort to grab and lift up.

After lifting the flap two more Phillip’s headed screws are revealed for removal.

The lower edge of the door panel can be grasped firmly and pulled away from the door to release the push pin retainers. Work your way across the bottom of the door and then up the side to the top of the panel.

With the bottom of the door panel pulled out about two or three inches, rotate the panel clockwise as shown in the picture below. This will allow the panel to be released from the door lock button.

Now tilt the top of the panel away from the door. The yellow clip has to be rotated away from the cable end. Then the cable end can be lifted up from the back side of the door handle.

Using a small screwdriver or similar tool gently lift the locking tab on the white retaining clip. Then slide th white retaining clip from it’s slot in the metal bracket.

Now that that is free you can better see the direction the yellow clip had to be rotated.

Almost there. Lift the harness from it’s perch on the inner door panel. this allows the panel to came away far enough that nothing else will be damaged while disconnecting the wiring harness connector.

With the door panel removed the inner metal bracket can now be removed. It covers the power door lock switch. There are four studs and this one had two nuts on each stud. They were 8mm or 5/16″.

There are two more Phillip’s headed screws along the lower edge.

The metal bracket is finally out of the way and I can now disconnect the power door lock switch. Lift the locking tab.

Pull the harness connector from the switch.  I went through and tested the red/black, orange/black, black, and white wiring between this switch connector and the power window switch connector. They were all okay. I reconnected the door panel harness to the door and installed the power window switch once again. The 5 volt reading was still low so that told me that the power window switch was indeed faulty. I also tested the power door lock switch and there is supposed to be less than 5 ohms resistance between terminal “C” and “D” when the switch is depressed in the lock position and between terminal “C” and “E” in the unlock position. In case you were wondering the yellow/black wire is for the illumination of the power door lock switch. The same test can be done at the power window switch connector between terminal 1 and 6&7.

Since the power door lock switch tests were out of range, I went ahead and installed a new switch. two 7mm screws hold the switch in place.

I plugging in the new switches and tested the system. All was good. I then installed the metal bracket and installed the door panel back onto the door.

I removed the old power window switch from the escutcheon plate as shown below.

The voltage readings with the new switches installed. A reading of 4.87 volts is good enough for me on a nominal 5 volt circuit. When the door lock switch a activated the 5 volt circuit will be pulled to less than one volt and close to zero.

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