NEED HELP Liftgate electrical problems

ts684

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It all started with a defogger that did not work. Same thing happened on my 04, turned out to be a broken wire. Took a look but couldn't find anything. Didn't have time to mess with further. The next day I found that the rear wiper wasn't working either. Also the remote fob didn't seem to be working correctly. Raised liftgate and a "ka-chunking" sound started. Turned out that sound was coming from a solenoid? that works a linkage to prevent the glass from opening when the liftgate is raised. I pulled the plug. Now I started probing with my DIMM. Had 12v on the orange wires at the Liftgate Control Module (LGM). Also 12v at the orange wire on the wiper motor. All black wires have a good ground. Purple wire that feeds grid is good to ground. Remote will usually unlock all four doors on second or third push, will not unlock liftgate. Outside rearview mirrors do defog. Something else, the radio and panel lights normally stay on after turning ignition off. Now it seems that happens only every other time I switch off, otherwise they go off at once. So, is it the liftgate module?? Any other tests I can do with a basic meter?
 

Mooseman

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Did you check the wires in the body to liftgate harness? They do tend to break in the rubber covering.

PXL_20210706_234126840_resized1493572480799714836.jpg
 

ts684

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Three orange, black ground, and purple to grid are all OK. Will Check smaller wires but will have to unwrap I guess. Any idea of how many other wires there should be? Is there a way to test lt blu data line? With only a DIMM.
 

Mooseman

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Could check for continuity from that lt.blue wire to the splice pack under the dash.
 

ts684

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This is what I did. Pulled out the connector that is in the upper section of the liftgate. There are 6 wires, is this correct? Three orange wires of different sizes, all 12v. One black ground, good ground. One brown wire that goes to the license lights. And one light blue wire, that shows 0.1v at the connector with igniton off. Unless there are more wires, it doesn't look like anything is broken.
 

ts684

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Forgot something. Had 0.1v at the blue wire with ignition off. With ignition on, voltage seemed to vary or pulse. Looks like I have contact thru all wires that pass into the liftgate. Should I look for a LGM in a U-Pullit? Should I try to get same year?
 

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These are some other On Topic LGM Legacy Threads that may have additional ideas and information:

https://gmtnation.com/forums/threads/almost-at-my-wits-end-with-the-lgm-please-help.5657/

https://gmtnation.com/forums/threads/03-trailblazer-lgm.9452/

The Splice Pack Continuity Check suggested by @Mooseman is a very good idea... but it has to be done at the one located under the small Carpet Cut Out under the Right Rear Passenger Seat.

*** Will Robinson (Robinson's Auto) shows you exactly how to check the System Module Connections from that very same Splice Pack and for both Front & Rear locations and from the BCM for PWM issues with all Modules on the Class 2 Network for any and all communication Issues that will be very helpful in this situation.

Trust Me... You won't want to miss watching this entire Video:



*** Pause on, Freeze Frame and then Screen Print the AllData Screens showing you what and where the Class 2 Network Splice Pack Wire Junctions, their Bi-Colors and the Connector Pin Positions are located.
 
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JerryIrons

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This might help you:

 

ts684

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Somehow my response seems to have disappeared. Have 12v at orange wire, ground is good. With igniton on have 2.3v at green wire regardless of switch position. Also had 12v there at one point but can't remember what I did. Neither remote unlocks the liftgate. One press does nothing, 2 or more will unlock 4 doors but not liftgate. Retained power takes turns working or not.
 

Mooseman

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Please use this FAQ article as reference however do not cross post to it.

Keep posting on this one for your problem.
 

ts684

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If I pick-up a LGM from a u-pull-it, will remotes work or have to be reprogrammed?
 

Mooseman

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You didn't mention the year of your truck. It should work however you have to be sure it has the remote lock option and the same year. If you can't find the same year, one change was in 06 or 07 where TPMS was added so select according to if you have TPMS or not.

You will have to reprogram all your remotes.

However, re-readng your initial post, I think your LGM is fine and that you may have a defective liftgate latch as you say this:
Remote will usually unlock all four doors on second or third push, will not unlock liftgate.
The remote not responding as it should could be either a weak battery or dirty contacts in the remote. Clean them and the carbon pads with alcohol. It is normal for only the driver door to unlock on the first push and all the doors and liftgate to unlock on the second push.
It all started with a defogger that did not work.
Check to see if power gets to it when it's turned on. If it does, it's likely that all the grids are broken. Very common issue on these trucks especially all except the two next to the wire contacts.
 

ts684

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All orange wires have power, all black wires show good ground. With defog switch on, there is no power on the purple wire at the LGM. There is some problem with liftgate latch. There is a linkage that rotates a tab so that the glass cannot be opened when the liftgate is raised. The solenoid for this linkage keeps "cachunking", not just once like it should. Wiper stopped working but shows power at orange and good ground. Readings at green wire are odd.
 

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Be advised that there have been some instances involving at least One of the Three Lift Gate Module Harness Connectors suffering from vibration induced Sparking Events occurring in between the Logic Board Metal Tines and those Connectors if they have worked loose over time. The resulting Electrical Arcing causes the Cadmium Coating to melt off exposing the underlying Mild Steel Tines to Rust up from Atmospheric Oxidation. Sketchy Electrical Continuity is the result.

It is possible to discover this problem by first unplugging the Three Connectors and removing the LGM from its mount point on the inner rear Lift Gate Door and carefully opening the Plastic Clam-Shell of the LGM to access the Logic Board inside. If this problem has been occurring, there will be Burn and Melting Marks in evidence where the Metal Tines pass through the Plastic Casement. Examine the inner contact areas of each Connector as well for related Arcing Damage.

Once this Corrosion and Rust is removed and any looseness in the inner holes-to-tines contact of the Connectors is dealt with along with the application of some Dielectric Grease, the LGM should once again work. However, finding a suitable, identical replacement LGM afterwards is a wise action to follow.

This Video addresses the R&R of the Lift Gate Electro-Mechanical Actuator Unit:

 

ts684

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Replaced lock/actuator with a U-Pull it from an 08 Envoy. No change, except that sometimes the ligtgate unlocks when it shouldn't. I have not gotten around to opening module yet. The U-Pull it had no 09 Envoys or Trailblazers and 08 part number did not match.
 

Mooseman

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What happens when you use the driver's lock/unlock switch? Same thing or it works as it should?

I can't imagine that there was much of a change between 08 and 09. Could try it and if it doesn't work, return it for a credit.
 

ts684

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Switch on driver's door works like it should, I think. Say that because once or twice I was sure I locked the doors, upon exiting, but the liftgate was unlocked. If I raised the gate to the point of hearing the cachunking sound the liftgate would then lock upon closing. Reading other posts I get the impression it might be a flaky ground eventhough it seems OK. Also, I noticed that when I hear the cachunking sound the license plate lights flash briefly and dim. Cachunking sound is a solenoid working a linkage that moves a tab to prevent gate glass from being opened when gate is raised. But it should only do this once, not continuosly.
 

ts684

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Since yesterday was a reasonably decent day weatherwise, I had a lot of other stuff to do than work on the Voy, but I did back it into the garage for a quick look. Raised the liftgate and it only cachunked once like it's supposed to, hmmm. Moved ignition to on but did not start. When I pressed the defog button, I heard a "clicking" sound likely from the LGM. More hmmm, but still no power in the grid. When I turned rear wiper to the first position I heard "something". Checking from outside, I noticed the wiper was moving back and forth about 1/4 inch. More hmmm. Hooked a couple of test leads together, used the rear shoulder belt bolt as a ground, and started touching several bolts on the liftgate. It was lowered at this time. Nothing happened until I touched a bolt on the wiper motor bracket, wiper did a sweep!! Could it be that I have a ground with gate up but not down?? Will look into it further today. Think I will run a new ground from body to liftgate and also splice into black ground wire in the liftgate. Hopefull that will cure all.
 

ts684

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Well, ran new ground from D pillar to liftgate with a branch spliced into the original liftgate ground wire. All orange wires still have power. Wiper now works!! Defogger grid is still dead, good to ground from purple wire, but no power. Forgot to note if anything was clicking. Also, fobs seem to be working better. I picked up an LGM from a 08 Envoy SLT, different part number, didn't try it yet. Will try opening original to see if everything looks OK.
Don't know if its related but four times since all this started, about 2-3 weeks ago, all warning lights come on except liftgate and CEL. Voltmeter, oil press, temp, and gas all go to zero. If i turn off and then back on everything comes back. This afternoon, not only was there no retained power, but everything went dead when I shut off, and door lock on driver's door did not work! Turned to ACC til everything lit, then turned off, had retained power then and locks worked.
 

Mooseman

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Don't know if its related but four times since all this started, about 2-3 weeks ago, all warning lights come on except liftgate and CEL. Voltmeter, oil press, temp, and gas all go to zero. If i turn off and then back on everything comes back. This afternoon, not only was there no retained power, but everything went dead when I shut off, and door lock on driver's door did not work! Turned to ACC til everything lit, then turned off, had retained power then and locks worked.
Your ignition switch may be on its way out. They go out so often that we keep a spare in the glove box. Cheap and easy fix.

For the defog grid, check the fuse/breaker in the back seat fuse box. I've seen it go bad.
 

ts684

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Well now with a better ground wiper works, have retained power, key fobs work, defogger does not. Looking at the original LGM the two adjacent contact for the larger orange wire and the purple wire look a bit melted. Tried the u-pull-it unit from the 08 Envoy. Now I have defogger plus everything else, except the fobs don't work. Would a remote reprogramming work? I"ll have to try that on Tue when I'm off again.
 

Mooseman

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Definitely have to program your fobs to this new LGM.
 

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