My Trailblazer's Electronics Freaked Out Today

l008com

Original poster
Member
Feb 19, 2016
896
Massachusetts
My truck has had no electronics related issues or anything similar to this or seemingly related to this. This all just happened out of the blue. . .

I drove about 25 miles to a mountain biking spot today. I used my 3rd key, the one with the small head, like from early 90's chevy trucks. As far as I know, this is just a regular key, I don't think TB's have valet mode right? So I drove up and everything seemed fine. I stored the bike on a bike rack but I opened the tailgate to unpack my gear, and re-pack my gear when I left.

As I was leaving the parking lot, the dome light was on. I made sure I hadn't turned it on, then I made sure all the doors were closed. All 5 were, and there was no message on the dash about it. But still, the light was on. So I hit the override button and drive home. Once i got home, I poked around more and here's whats happening:

- The dome light turns on and stays on. While you are driving, it's on. When you get out, it stays on until the timer shuts it off after many minutes. The override will turn it off but beyond that, nada.

- As soon as you turn the engine off, the power windows and interior lights immediately shut off, as if you have a door open. But none of the doors are open, and the dash doesn't warm me about any.

- As soon as I start driving, my TPMS starts freaking out, telling me I need to service the system. I do sometimes get "Service TPMS" messages after a half hour or more of driving, but I haven't in a while. Now it happens as soon as I turn the truck on. It's enough to make me think it's part of this malfunction.

- I cannot open my tailgate. The lock and unlock buttons on the doors work on all the rest of the doors, but they won't unlock the tailgate. Luckily my bike was on a bike rack, otherwise it would literally be stuck in my truck. Is there some emergency release for the rear gate? I am of course going on vacation in a few days and I will need to get in the back. Also, the glass won't open when you push the button.

- My key fobs don't work! They always worked fine. Now no response at all, lock or unlock, no matter how close I am to the truck.

All of this literally happened all at once. I feel like my truck's computer crashed and needs a reboot, but it reboots every time you start it up, right? Or should I try disconnecting the battery and seeing what happens? Or is this a sign of something else entirely? Could I have somehow put my truck into valet mode and now it's stuck there? Note that once I got home, I stopped using the small key and want back to my normal every day key but no change.

Some symptoms sound like the problem may simply be a door open sensor on the liftgate not working. But if that were the case, that shouldn't affect the remote locking and unlocking the doors, right? And sure wouldn't affect the TPMS!? It just makes no sense.
 

budwich

Member
Jun 16, 2013
2,050
kanata
your wiring to the lift gate module is fubarred.... it likely happened during your last "open / closed". Basically, the wiring gets brittle from age and open / close actions cause breaks and / or shorts. Others will tell you how to "emergency open" the lift gate via a manual release.
 

Mooseman

Moderator
Dec 4, 2011
25,350
Ottawa, ON
Splicing should suffice. The fun is finding the broken wire. Pull and tug on each one inside that boot as the copper strands can be broken inside the insulation.
 

l008com

Original poster
Member
Feb 19, 2016
896
Massachusetts
Is there a circuit/fuse I can pull that will deactivate the lift gate, and allow everything else to return to normal operation until I get around to fixing this, which will be a few weeks at best.
 

Blckshdw

Moderator
Nov 20, 2011
10,685
Tampa Bay Area, FL
Is there a circuit/fuse I can pull that will deactivate the lift gate, and allow everything else to return to normal operation until I get around to fixing this, which will be a few weeks at best.

The disconnection of communication between LGM and the rest of the truck, is causing the problem. Disconnecting anything else won't fix that. You're gonna have to get in that rubber boot, locate the broken wire, and repair it.
 
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l008com

Original poster
Member
Feb 19, 2016
896
Massachusetts
So today I popped open the secret hatch, hit the lever, unlocked, and opened the rear hatch. As I touched the rubber boot, things were flipping on and off, and unfortunate zapping sounds were heard. I think it's safe to say you were right, my problem is in that boot!

But that led me to my next problem.... how do I get at the wires IN the boot? The wires go through it so there doesn't seem to be any way to get at the wires besides cutting the boot open, but I definitely don't want to do that! It feels like there is little if any slack in the wires so I can't just pull them out?
 

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Blckshdw

Moderator
Nov 20, 2011
10,685
Tampa Bay Area, FL
You don't need to remove the boot completely, just get it out of your way. The same way you detached the top from the lift gate side, is the same way you detach the bottom from the body side. Slide the boot towards either side to access different sections of the wire so you can investigate further, and repair as needed.
 
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l008com

Original poster
Member
Feb 19, 2016
896
Massachusetts
Update: I took apart the boot and at first I couldn't find any bad wires. I was very confused because sometimes even touching that boot has caused power locks to click, so clearly the problem was there. After messing with it a bit, suddenly there was a broken wire, then another, then another.

I am not a strong solderer in normal situations. But doing it in that tiny cramped space with essentially NO slack in the wires was not easy, and I hope my connections hold but I wouldn't be surprised if they did not. That said....

TPMS now working normally.
Dome light now working normally.
Remotes now working normally.
Lock in liftgate now working normally.
Accessory power now working normally.


Note that the image attached is not a final solder. I fixed that one up a bit. It was so hard keeping the wires together, with no slack in the lines and no room for clips. Ugh I hate soldering so much.
 

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Blckshdw

Moderator
Nov 20, 2011
10,685
Tampa Bay Area, FL
Glad you were able to find the broken wires. In cases where there's not enough wire to make good contact for a repair, you can always splice in a short length of spare wire to cover the gap. That method would also allow you to be sure you were able to cut out all of the damaged wire. That helps more in situations like burnt/melted wires, than broken ones from flexing.
 

christo829

Member
Dec 7, 2011
501
Fairfax, Virginia
(Ha! Blckshdw for the scoop! :smile: )

What I've done in the past for tight space/no slack issues is get same gauge wiring and splice a small extension in to the broken wire. I used the new wire section in the area that got the most abuse, using the old wire as a pull line once I had one side soldered. Had to do that on my old
S10 Blazer rear hatch.

It's a bit more painstaking, but the extra wire length gives you some flexibility to get a better solder joint, and you're not trying to put the repaired section back close to the flexing part of the hatch wiring passage.

Cheers-

Chris
 

l008com

Original poster
Member
Feb 19, 2016
896
Massachusetts
Question: If this happens again, can I just take the body panel off the inside of the liftgate? then pull the whole harness back? That should make it MUUUUUUCH easier to solder the wires, if I ever have to again.
 

Blckshdw

Moderator
Nov 20, 2011
10,685
Tampa Bay Area, FL
It's your truck, you can do anything you want if you believe it will make maintenance/repairs easier. :yes:
 

l008com

Original poster
Member
Feb 19, 2016
896
Massachusetts
Well ok but I guess teh question is, WILL it? Is the gate's harness easily accessible with the paneling removed? It sure seems like it would but I don't really want to go rip the inside apart just to test.
 

Blckshdw

Moderator
Nov 20, 2011
10,685
Tampa Bay Area, FL
I don't really want to go rip the inside apart just to test.

You pretty much have to do this...

Is the gate's harness easily accessible

In order to answer this question accurately, since "easily" is a relative term. No one has ever done that, to fix the boot wiring issue, so the amount of work removing both of the panels, locating all the clips, and undoing them, may not be worth the time saved on the wiring, since you spent it inside the gate.

But in your case if you don't feel strong on your soldering skills and really want the extra slack, then maybe that extra time would be worth it to you. Only way to know for sure is to look in there to see how many clips there are, and if you're able to release them easily.

Edit: You may get away with just removing the upper panel, getting a little slack there, depending on how much of the harness you want to pull. Not sure what you'd do though if the damage was closer to the body side of the boot. No idea how much of the harness is secured between the headliner and the roof
 
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