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Discussion Starter #1
My wife called from work this afternoon saying that her key fob would not unlock the doors on her 2019 Acadia SLT. She was able to pop the hatch and climb through (We didn't realize there was a hidden key in the fob).

Symptoms are as follows:
  • No Lock/Unlock function on key fob but do get the horn honk and lights flashing as if it's receiving a signal
  • Electric door lock switches in the cabin do not function, windows and other door controls function normally
  • Key fob works to remote start (which requires the lock button to be pressed), rear hatch, panic
  • Tried to reprogram without success
  • I washed the vehicle yesterday (nothing fancy, just garden hose), then cleaned under the hood with degreaser. FOB functioned fine when she parked at work this morning.
  • Temperatures have been around freezing but I don't see that as the issue
  • Changed batteries in the remote with no change
  • I looked in the owner's manual but it appears that the lock circuit is on the fuse with something else. It appears that everything else functions normally from what I can tell so I sort of rule out a fuse issue.
I've read a little bit about the remote control receiver module but it strikes me as odd that the only two functions that don't work are the lock/unlock. Even then, it appears the vehicle is receiving the signal, it's just not mechanically operating the lock actuator. I suppose I'll poke around on it a little bit more before we schedule a dealer visit. Thanks in advance to anybody who might have an idea.
 

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If the lock/unlock does not work using the interior switches either, then it seems isolated to just that since the remote start, lights flash when buttons are pressed, etc.
Maybe check each door switch and see if each "feels" the same or may be stuck down in one position.
Each switch should spring back up after pressing. Also, check and operate the Child Safety disable switch on the drivers door.
Otherwise. . . it should still be in warranty?
 

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Discussion Starter #3 (Edited)
If the lock/unlock does not work using the interior switches either, then it seems isolated to just that since the remote start, lights flash when buttons are pressed, etc.
Maybe check each door switch and see if each "feels" the same or may be stuck down in one position.
Each switch should spring back up after pressing. Also, check and operate the Child Safety disable switch on the drivers door.
Otherwise. . . it should still be in warranty?
Thanks. I did check the child lock and all of the switches. They seem to feel normal. We're just out of warranty at 42k miles. We bought the vehicle used last year. I don't mind eating the repair but always kick myself when it ends up being something stupid! I was also thinking a relay but I can't find one that seems to control the door locks (even though I'm sure there is one)
 

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Thanks. I did check the child lock and all of the switches. They seem to feel normal. We're just out of warranty at 42k miles. We bought the vehicle used last year. I don't mind eating the repair but always kick myself when it ends up being something stupid!
It is puzzling. I looked at my 2019 Owners Manual and don't see a particular set of fuse or fuses for door locks.
It is a BCM function. . .. so maybe carefully check each of the BCM fuses.
There are several.
Best to take them out and check using a multimeter or continuity checker. They can be difficult to tell if they are good or bad visually. At least for my eyes.
 

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... I don't mind eating the repair but always kick myself when it ends up being something stupid! ...
These vehicles are chock full of stupid things. They're designed by common-core educated "engineers" and computer gamers. What else could you expect from them? :devilish:
 
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Discussion Starter #6
It is puzzling. I looked at my 2019 Owners Manual and don't see a particular set of fuse or fuses for door locks.
It is a BCM function. . .. so maybe carefully check each of the BCM fuses.
There are several.
Best to take them out and check using a multimeter or continuity checker. They can be difficult to tell if they are good or bad visually. At least for my eyes.
I did the same thing. I poured over the fuse diagram thinking something would change every time I looked at it haha. Checking the BCM fuses is a good idea. I'll give that a shot. Looks like this is a fairly common issue. There are a number of YouTube videos on it including a 2020 that's only a week old.

 

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... I was also thinking a relay but I can't find one that seems to control the door locks (even though I'm sure there is one)
K1 and K2 in the rear compartment fuse box are the only relays I found that are remotely associated with vehicle 'body' functions. Many of the fuses there protect passenger compartment body circuits.
 
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Discussion Starter #8
Update...I went through all of the BCM fuses with no luck. I thought I had stumbled on something in the rear fuse box because I can hear the relay firing when I click the remote. Looking back, I think this may just be for the tail lights flashing. I couldn't, however, locate the actual relay in or around the fuse panel. I also noted that the physical button on the rear hatch does not operate the hatch to close. I assume that this may be on the same circuit as the door locks. I'll keep searching and post back if I come up with something.
 

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Discussion Starter #9
Well second update this morning. I decided to check the truck this morning on the way out of the door to work. It appears everything is working fine this morning. I’m thinking some type of moisture or water intrusion into the wiring somewhere. I may do some testing with the garden hose if I have some time.
 

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I've experienced this too. Along with my strange tail lamp issue that I've posted about before, about a week ago, my lock issue was just like you described...to a T! The fob would flash the lights/horn when locking, but nothing happened. Or, it would lock, but not unlock. I checked the inside buttons, nothing. Then later that day they worked....kinda. Then a day later, back to not working. I could tell it was a computer issue when I would hit the lock on the fob, when all the lights are supposed to flash and horn chirp, only SOME of the lights would flash...and then they would a little staggered at that. Strange. They have been working for a week now fine. I'm telling ya, it's gotta be something up with the BCMs in these things. Strange electrical gremlins for sure. I don't know what else to check. I'm gonna have to bite the bullet and take it to the dealer and tell them my issues. My luck will have it that it all works fine when they get it though. Ugh.
 

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My wife called from work this afternoon saying that her key fob would not unlock the doors on her 2019 Acadia SLT. She was able to pop the hatch and climb through (We didn't realize there was a hidden key in the fob).

Symptoms are as follows:
  • No Lock/Unlock function on key fob but do get the horn honk and lights flashing as if it's receiving a signal
  • Electric door lock switches in the cabin do not function, windows and other door controls function normally
  • Key fob works to remote start (which requires the lock button to be pressed), rear hatch, panic
  • Tried to reprogram without success
  • I washed the vehicle yesterday (nothing fancy, just garden hose), then cleaned under the hood with degreaser. FOB functioned fine when she parked at work this morning.
  • Temperatures have been around freezing but I don't see that as the issue
  • Changed batteries in the remote with no change
  • I looked in the owner's manual but it appears that the lock circuit is on the fuse with something else. It appears that everything else functions normally from what I can tell so I sort of rule out a fuse issue.
I've read a little bit about the remote control receiver module but it strikes me as odd that the only two functions that don't work are the lock/unlock. Even then, it appears the vehicle is receiving the signal, it's just not mechanically operating the lock actuator. I suppose I'll poke around on it a little bit more before we schedule a dealer visit. Thanks in advance to anybody who might have an idea.
I just had this issue with my 2018 gmc acadia. They had to replace wires and plugs. They said I had water damage due to my third break light leaking water. Its very frustrating and expensive.
 

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I just had this issue with my 2018 gmc acadia. They had to replace wires and plugs. They said I had water damage due to my third break light leaking water. Its very frustrating and expensive.
What other symptoms did you have?
 

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What other symptoms did you have?
I first noticed water inside my back window after I went through a car wash. Two days later my fob died. Changed batteries but my main power switch nor my fob worked. The ran diagnostics and found some electrical codes were showing water damage. They replaced 4 body plugs and wires and the third break light had to be replaced! Nothing was covered under warranty due to water damage. It was a 700 dollar repair. I just got my car back after a week! Very frustrating 😕
 

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... Nothing was covered under warranty due to water damage. It was a 700 dollar repair. ...
Your B2B warranty had expired by then? Water leaks should have been covered by that, unless it was an owner-caused condition.
 

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I bought a 2017 Denali about 3 months ago. I have had weird electrical problems 3 times since I owned it. First the radio screen was half blacked out where several things were missing that were normally there. Shut down and restart fixed it. The second thing was the door locks would not open with the fob. Restarting did not fix it. Unhooking battery and reconnecting fixed it. The 3rd time, the display in front of the steering wheel stopped communicating with the main console. The steering volume controls did not work, no speed limit display, no access to radio. Unhooking battery fixed this.

The common thread was a car wash right before each incident with undercarriage spray. I read somewhere that there is a TSB that indicates a potential water inlet problem in the rear driver side module that contains the blind spot and other sensors. The TSB indicates the problem causes swelling and interferes with the CAN bus, which is why I believe the problems manifest as strange electrical/network issues (everything in these cars is on the network bus).

Knowing how much of a pain it would be to prove to the dealer that there is a problem, plus the inconvenience of going there, I decided to cover the opening under the sensor module with duck tape. I cleaned it well with alcohol first and covered the open slit on the bottom securely with tape.

I have had several car washes since and have not had a single problem for a couple of months now.
 

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I bought a 2017 Denali about 3 months ago. I have had weird electrical problems 3 times since I owned it. First the radio screen was half blacked out where several things were missing that were normally there. Shut down and restart fixed it. The second thing was the door locks would not open with the fob. Restarting did not fix it. Unhooking battery and reconnecting fixed it. The 3rd time, the display in front of the steering wheel stopped communicating with the main console. The steering volume controls did not work, no speed limit display, no access to radio. Unhooking battery fixed this.

The common thread was a car wash right before each incident with undercarriage spray. I read somewhere that there is a TSB that indicates a potential water inlet problem in the rear driver side module that contains the blind spot and other sensors. The TSB indicates the problem causes swelling and interferes with the CAN bus, which is why I believe the problems manifest as strange electrical/network issues (everything in these cars is on the network bus).

Knowing how much of a pain it would be to prove to the dealer that there is a problem, plus the inconvenience of going there, I decided to cover the opening under the sensor module with duck tape. I cleaned it well with alcohol first and covered the open slit on the bottom securely with tape.

I have had several car washes since and have not had a single problem for a couple of months now.
Where exactly is the module? In the cargo area on the left side with the fuse box?
 

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The module is on the outside of the car on the rear driver's side up near the left exhaust pipe inside the rear body panel. It is a flat black plastic "box" mounted inside the body panel, but accessible from under the car. This is what I believe water was spraying into and causing problems.

You can see it if you look up from underneath where the exhaust is. There is only one on the driver's side.
The bottom of it has an open slot that lets water in. That slit is what I covered.

My blind spot still works fine, and the kick open hatchback also still works fine with it covered.
 

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The module is on the outside of the car on the rear driver's side up near the left exhaust pipe inside the rear body panel. It is a flat black plastic "box" mounted inside the body panel, but accessible from under the car.
Is that the liftgate foot activation module, or one for the SBZA system? If SBZA, one should also be present in the same area on the right (passenger) side.
 
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