Liftgate Control Module

Gix1k4

Member
Feb 9, 2014
9
I'm going to admit a mistake on my part to hopefully help anyone else avoid doing it. We recently had out TB in the shop for a new transfer case (imagine that, lol) and a few days after we got it back my g/f noticed that the rear wiper wasn't working. I followed all the steps mentioned in the thread, including checking the fuse...... except I was looking at the circuit breaker and not the fuse. The spot where the fuse is supposed to be was empty, and in my haste I didn't catch it. The shop must have pulled it when they were doing their diagnostics on the tccm and encoder motor before they realized that it was a catastrophic internal t-case failure.

Long story short....Take your time and work methodically. :blush: :duh:
 

Real McCoy

Original poster
Member
Jul 31, 2013
50
Another wire broke! I recently noticed the rear wiper wasn't working so I immediately suspected the broken wire between the liftgate and body. Quick check with the multi-meter and I confirmed no voltage from one of the orange wires at the connector. Spliced the wire and wiper works just fine now - whole repair took 15 minutes or less. 297,000 miles and counting.

Doug
 

KSPNM

Member
Mar 3, 2015
2
Hi. I have a 2002 Trailblazer and would like to check the continuity of the wires running from the rear fuse box to the wiring harness at the top of the lift gate.
Any suggestions on how to do this?

Thank you,
Amy
 

AtlWrk

Member
Dec 6, 2011
674
There are six wires in the harness running to the lift gate: 3 orange (battery 12V+), one black (ground), one brown (license plate light supply +12V when parking lights are on) and one blue (data bus).

If you remove the panels in the lift gate you'll find the lift gate module (LGM). One of its connectors has two orange wires (Battery +) and black (ground) (and purple for defrost, not important here). The rear wiper motor also has an orange and black wire.

You can check each orange wire relative to ground (black wires) and should have battery voltage 12V+. Note: don't check relative to the sheet metal of the lift gate, it's not a reliable ground. Also know that broken wires may not break their insulation and could show continuity when flexed a certain way so grab the harness boot and give them a wiggle when doing this inspection.

If your license plate lights are working and your rear wiper works then you know those wires are fine too.

Are you having any specific symptoms? We could narrow down where to look.
 

KSPNM

Member
Mar 3, 2015
2
Thank you for the reply.

I've checked the wires running from the harness out to the lift gate module and they all appear to be working correctly.
What I'd like to do next is check the continuity of the wires the other way: from the harness back through the body to the rear fuse box.
Do you know how that can be done?

Also, how can I check that the black and blue ground wires are not broken inside the boot somewhere?
Can you explain a bit more about how to give them the "wiggle"?

The hatch to my rear lift gate, rear defroster, rear wiper and key fob are not working. My license plate lights are also not coming on, but I have not tried to replace the bulb.

Thanks again.
 

AtlWrk

Member
Dec 6, 2011
674
Ahh! the key here is that your license plate lights aren't working either. The only thing they have in common with the LGM is the ground. It sounds crazy but look very closely at your license plate lights while locking/unlocking your truck with your keyfob. If you see a faint flicker then you can be certain that the ground wire in the boot is broken.

You need to pull the boot back from the body and lift gate and carefully inspect as much of the wires as you can visually. Personally I'd focus on the black ground wire but check them all. It may not be obvious if only the wire broke and not the insulation surrounding (it happens). You can check continuity between the black wire at the lift gate module and the ground point on the rear most pillar on the driver's side inside the trunk area. You'll probably have to pull the trim piece off to get to it.
 

USA-1

Member
Dec 8, 2013
19
Replaced the rear wiper motor and the wiper switch, still no results. have power to the large orange wire not the small one going to the wiper motor. Fuse is good and has power going to it. Going to try and follow power to a break in the wire. Wondering if someone else ran into a similar problem?
 

IllogicTC

Member
Dec 30, 2013
3,452
USA-1 said:
Replaced the rear wiper motor and the wiper switch, still no results. have power to the large orange wire not the small one going to the wiper motor. Fuse is good and has power going to it. Going to try and follow power to a break in the wire. Wondering if someone else ran into a similar problem?
You mean the small green one? That's because the LGM doesn't supply constant voltage on that line, it sends a PWM signal to the wiper assembly which in turn decides delay rate. The proper way to measure the dark green wire would be to measure its duty cycle, as you'd be more likely to get a proper reading.

The LGM supplies the PWM signal by presenting ground to the green wire (the hot is via that big orange wire), meaning that if the LGM isn't properly grounded, it can't tell the wiper to do something.

If the circuitry for supplying the PWM signal in the LGM is faulty, the wiper won't run.

If the LGM is not receiving the Class 2 data from the BCM to engage the wiper, it won't run.

The washer runs on an entirely separate circuit, being a pump up front which is activated by the BCM.
 

USA-1

Member
Dec 8, 2013
19
Found a broken orange wire suppling power to the motor. The break was in the boot from the liftgate to the body. On the bright side I now have a spare switch and motor. Crap!!!!! Its still cheaper than going to a dealership.
 

IllogicTC

Member
Dec 30, 2013
3,452
USA-1 said:
Found a broken orange wire suppling power to the motor. The break was in the boot from the liftgate to the body. On the bright side I now have a spare switch and motor. Crap!!!!! Its still cheaper than going to a dealership.
Could always watch for someone needing a new switch or motor on here. Good opportunity to make a few bucks back if you don't want to keep them in inventory. Thanks for the feedback, that boot is a real wire-killer, it's just that it's usually the Class 2 Data wire.
 
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USA-1

Member
Dec 8, 2013
19
For what this truck has cost me, I will leave the new parts in it. It is the guide of this site that helps find a solution to a problem. This has become a very valuable source to find a solution.
 
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breckbrew

Member
Apr 7, 2015
4
Went camping last weekend. Got something out of my Envoy and noticed that the lights weren't going out. Next day I noticed the key fobs didn't work. After that I noticed the radio shut down as soon as I turned the engine off and the rear wiper didn't work. Came on here and found out where to look. Sure enough the blue wire is completely severed and one orange and one black are pretty close.

For those that have spliced the wires, how did you do it? Pigtail seems like it would not fit back in, in-line could work I suppose, but not much room to work with. Did you add additional wire? Solder?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
breckbrew said:
For those that have spliced the wires, how did you do it? Pigtail seems like it would not fit back in, in-line could work I suppose, but not much room to work with. Did you add additional wire? Solder?
Soldering would be your best bet, if at all possible. Crimp on butt connectors would be OK to use in a pinch, or as a temporary fix. You could add wire to it if you needed to, but that wouldn't be required unless maybe you had 2 cuts in the wire to repair.
 

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