Mysterious door lock issue

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Dutchman

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It's me again....

Problem 1: One of the things on my list to update/fix was the power door locks for the rear doors and liftgate. So, I got the liftgate actuator and just hadn't gotten around to replacing it. The other day, I noticed that as I locked the doors with the fob, I heard ALL the doors lock for the first time. I thought, "Maybe it's going to start working". But, NO! The doors locked, but now the rears and liftgate would not unlock. :mad:

So, it was time to fix it. I managed to get the liftgate open, thanks to this Youtube video. I got the panels off and decided to plug the new actuator in before removing the whole mechanism just to make sure it would work. It did not. So I started combing the forum for possible fixes and found something about the relays being bad.

I went to the parts store and got two new relays. I pulled the relays as I went in, just to make sure I got the right ones. I didn't try to lock the doors, because I had the relays in my hands, so surely the door locks wouldn't work.... As I returned to the truck, new relays in hand, I instinctively pushed the button to unlock the doors. As soon as I did, I thought that was silly, they won't work. BUT..... they did. The front door locks cycled to unlock with no door lock relays in the fuse panel. WTH!?!?!

I replaced the relays and tried again, only to get the same result. The front doors work perfectly. The back doors and liftgate don't do anything. Just on a whim, I checked the lock fuse, thinking, obviously it's okay because the front doors work. Well, the fuse was good, but with it out, I tried the door locks and the front doors STILL WORKED!!!

What's going on?? I pulled the relays and the lock fuse and the front door locks still work!! Has somebody rewired something screwy?

Problem 2: A few weeks ago, when I had the dreaded "Reduced Engine Power" message, I could not get my scanner to read the code. I found that the fuse providing power to the port was blown. After I changed that and cleared the code (which hasn't come back again...yet), now the horn doesn't work. What I mean by that is that when I push the center of the steering wheel, nothing happens. But when I lock the doors (front doors at least) with the remote by pushing the button twice, the horn honks. When I push the unlock button twice, the horn beeps two times. I just can't blow the horn at the dumb drivers I pass on the road.

Any feedback on either or both of these issues would be greatly appreciated.
 

TEXCHEVY

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I don't know if it will help, but last year I had a similar problem in my 2001 Chevy Tahoe . My mechanic friend disconnected the positive and negative battery cables, then joined them for 10 seconds, left the battery disconnected for more 20 minutes, once I reconnected the cables to the battery my problems are gone.
 
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Dutchman

Dutchman

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Oct 19, 2020
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Charlotte, NC
After some digging around in the wiring diagrams, I found that the rear doors and liftgate locks go through the BCM, but not the front door locks. That explains some of the stuff I noticed, but might mean I need to replace the BCM. @TEXCHEVY, thanks for the info. I'll try that before I look at replacing the BCM. It would save me a few dollars if it works, and nothing if it doesn't. ;)
 

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