Door locks no workie

[Lane99tahoe]

Ok so I saw an earlier thread on this topic from like last week and didnt want to hijack it so im starting fresh.

I have 99 hoe, and only my driver pwr door lock isnt working. All 4 motors are good, switches are good, relay under dash by gas pedal is good.

Heres whats baffling to me. The motor/actuator has tan and grey wire going to it. Both wires get 12v when pressing lock button, either wires get voltage pressing unlock! Wtf????

 

[Lane99tahoe]

Anybody?

 

[SunlitComet]

one wire should have positive voltage and the other negative voltage. which one depends on whether you are locking or unlocking.

 

[Ponchonutty]

Correct /\. You have reverse polarity. More than likely you have a broken wire inside the door boot if all other locks are working correctly. when one wire shows 12v the other should show ground and so forth. You could also have a bad relay for the driver priority unlock system too. Unplug the motor and then test it again and see which wire doesn't change state when either pressing lock or unlock. I believe the rest state is ground?

 

[Ponchonutty]

 

[SunlitComet]

what bad relay for the driver for what priority unlock system?

 

[Ponchonutty]

You can set up the locks to unlock only the drivers door then if you quickly press unlock again does the rest. If that lock isn't doing anything, it more than likely is a bad wire

 

[SunlitComet]

hmm, no such thing on the gmt400 platform with a possible exception of it being a luxury model. otherwise the only thing that would unlock and only unlock the drivers door is the keyless entry system.

 

[Ponchonutty]

Correct. It would be along with the factory keyless system. Sorry but it's been a while since I've worked on an older Tahoe. Do what I said on unhooking the motor harness then test each wire to see which wire doesn't change state when pressing the lock/unlock buttons