Liftgate Control Module

[Real McCoy]

I have experienced what appears to be a failure of the Lift Gate Control module. I have a 2002 TrailBlazer LS, standard wheelbase. I have checked with a multimeter and confirmed a good ground and 12 v through the wires to the lift gate and there is no evidence of broken wires.

Based on the need to dealer program a new module I am looking for a used one that apparently can be used plug and play with existing programming. I have located a module for a 04 EXT long wheel base and want to know if that is the same part that is used on the short wheelbase.

Thanks for the help.
Doug

 

[The_Roadie]

Welcome! The only odd duck is the Envoy XUV. Other vehicles share the same LGM and the functions are the same. Just checking to make sure you know you have a good data communication wire, since it can flex and break inside the wire insulation hidden by a rubber boot up at the liftgate hinge line and not be obvious.

Assume you've just lost the use of the remote unlock function, rear wiper, and defogger. If the license plate lights are dead as well, it may be multiple broken wires or a bad ground.

 

[Real McCoy]

Thanks for the quick reply on the LGM.

I will double check the data wire. Is there a test I can do with my digital multimeter? Will I see +/- 5v or can I check continuity to BCM connector?

Thanks
Doug

 

[The_Roadie]

It's a shared bidirectional data bus with no DC voltage on it normally. Only way to see much is with an oscilloscope. You could check continuity with the power off to one of the two data comm splice packs discussed in other threads.

 

[Real McCoy]

Thanks.

 

[Gevans17]

I have experienced what appears to be a failure of the Lift Gate Control module. I have a 2002 TrailBlazer LS, standard wheelbase. I have checked with a multimeter and confirmed a good ground and 12 v through the wires to the lift gate and there is no evidence of broken wires.

Based on the need to dealer program a new module I am looking for a used one that apparently can be used plug and play with existing programming. I have located a module for a 04 EXT long wheel base and want to know if that is the same part that is used on the short wheelbase.

Thanks for the help.
Doug

I used a used 2008 LGM in my 2002 TB. Works fine

 

[Real McCoy]

Roadie,
After a couple of weekends too busy to check further, I finally confirmed the blue data line has continuity from the data splice block under the seat to the lift gate module in the tailgate. I rechecked the ground and power, both good.

From what I have read, I believe this leaves me with the conclusion that the liftgate module is bad. I was wondering how familiar you are with the electronics on the board - I had one of the engineers at work take a look at the board. The only thing that he found was that the clock would run initially as he applied power but then would stop. His question was weather that would be normal or possibly the cause of the failure. Any thoughts?

I have located a used module locally and can pick it up tomorrow, but have doubts about buying used electronics. Do you think used is the way to go or should I spend the bucks for new and dealer programing?

Thanks
Doug

 

[The_Roadie]

I've never had a problem with the LGM and haven't looked inside mine. Sorry. I would have no problems buying a used one as long as the seller guarantees it in some way.

 

[Real McCoy]

Thanks for the reply.

 

[Real McCoy]

Quick update - went to pick up the used liftgate module today and asked about a guarantee. Since I had the vehicle there with the guts exposed he offered to plug it in to see if it worked before I bought it. We plugged one in and still nothing worked. Okay, so maybe it was bad so he had another vehicle in the yard and offered to get the liftgate module from that one. Well the second one didn't work either. While possible, it is unlikely both were bad so I guess I am chasing something else that is keeping this from working. Oh, he didn't insist I buy the module either, but for $35 I decided to buy it just in case. If I get this all figured out and don't need it I can sell it.

I will be studying the wiring diagram again and re test everything I already did.

Doug

 

[budwich]

what function (s) are you chasing / missing? Pick one and "chase" that entirely thru. I guess anther question would be how did you check for ground? And related, yes you tested with a meter, but that those condition only "suggest" potentials, but don't necessarily indicate current carrying capabilities. It is possible that the potentials are there but poor conductivity results in little / no current.... maybe. Just a thought, I haven't look at the diagram. Not sure about the "long termness" of the programming... is it possible that the replacement unit(s) may have been sitting too long or don't have the appropriate options?

Of course, lastly, you did check ALL your fuses.... not just the one(s) labelled for "LGM" or something nice like that...

 

[Real McCoy]

Well, Just want to follow up on the liftgate module issue. As I expected, once the two used modules did not work, I had a broken wire. What threw me off was the info I had indicated that there were two orange wires in the harness that goes from the body to the liftgate, and that they both had power. Turns out the harness on my TB has 3 orange wires, all three need to be hot with 12VDC, and one wasn't -= I missed that point since I was only looking for two hot and found two hot. So once I found the break and spliced it my original liftgate module worked just fine.

Thanks for the help
Doug

 

[The_Roadie]

Thanks for the come back. I neglected to ask if you had THREE hots because at least you said you checked "wires" for 12V, and I thought you had the schematics and knew there were three hots. I gotta remember to be explicit more if I'm gonna help save people time and money.

 

[Real McCoy]

Roadie,
The red face should be for me cause I should know better. I was in a rush and didn't think it all through. You and the others have been a tremendous help as the TB gets older and needs more help. Thanks again.

 

[mrjean]

question on this.
my rear defoger actually doesnt work (it was working when i bought the car used) and my wiper/water works whenever it feels like. i have not lost my keyfob lock/unlock (unless the car still beeps when i lock the door and yet the window/trunk remain unlock, this would suck as i dont live in the safest neighborhood).

i just bought a multimeter ms8268 however where the heck are the wires for me to check?
i knew it would be trouble since the third brake light panel screws are rotted and flap when theres high wind or when i take the power wash to it. ill see if i can take a pic of what im talking about tomorrow.

but, would that cause the rear defog to not work? i believe i have checked all fuses although i dont remember which i checked since it was a whiles back.

 

[The_Roadie]

The LGM has THREE hot wires to check. Have you downloaded the schematics yet?

 

[christo829]

question on this.
my rear defoger actually doesnt work (it was working when i bought the car used) and my wiper/water works whenever it feels like. i have not lost my keyfob lock/unlock (unless the car still beeps when i lock the door and yet the window/trunk remain unlock, this would suck as i dont live in the safest neighborhood).

i just bought a multimeter ms8268 however where the heck are the wires for me to check?
i knew it would be trouble since the third brake light panel screws are rotted and flap when theres high wind or when i take the power wash to it. ill see if i can take a pic of what im talking about tomorrow.

but, would that cause the rear defog to not work? i believe i have checked all fuses although i dont remember which i checked since it was a whiles back.

Hopefully you checked those fuses with the meter?

You still need to check for continuity through the wiring to the defrost grid and out to ground. You can have all the power you need at the fuses,
but if there's no ground, there's no place for the current to go, assuming it's reaching the grid in the first place.

If you've got intermittent wiper function, that points more definitely to a wiring issue. As Bill pointed out, download the
wiring diagram and make sure you've got the power actually reaching the grid.

Good Luck!

Chris

 

[sawicksted]

Hopefully you checked those fuses with the meter?

You still need to check for continuity through the wiring to the defrost grid and out to ground. You can have all the power you need at the fuses,
but if there's no ground, there's no place for the current to go, assuming it's reaching the grid in the first place.

If you've got intermittent wiper function, that points more definitely to a wiring issue. As Bill pointed out, download the
wiring diagram and make sure you've got the power actually reaching the grid.

Good Luck!

Chris

I had to "fix" the grid on my 03 TB. Continuity is the way I figured out what was wrong with mine - seems the owner before had scratched the grid with something from top to bottom only it was barely noticeable so....bought a special paint kit for the grid and it was back up and running after an hour or so.

Again check to make sure you got power to the grid first. Good Luck with that.

Scott

 

[sawicksted]

question on this.
my rear defoger actually doesnt work (it was working when i bought the car used) and my wiper/water works whenever it feels like. i have not lost my keyfob lock/unlock (unless the car still beeps when i lock the door and yet the window/trunk remain unlock, this would suck as i dont live in the safest neighborhood).

i just bought a multimeter ms8268 however where the heck are the wires for me to check?
i knew it would be trouble since the third brake light panel screws are rotted and flap when theres high wind or when i take the power wash to it. ill see if i can take a pic of what im talking about tomorrow.

but, would that cause the rear defog to not work? i believe i have checked all fuses although i dont remember which i checked since it was a whiles back.

I just bought an 06 that had the Lock issue but it was a frozen pivot arm and not the wiring. Yes all the other doors locked and the Horn would beep but you could open the glass or the hatch after locking all the doors and no alarm would sound.
I found out before I lost anything - I was away camping with all my camera gear, two laptops, 2 cell phones and wallets in the truck while out hiking. I came back and lifted the glass - Thinking I had just unlocked the doors but my wife couldn't get in to the TB on the passenger side and that's when I realized the issue after trying different lock / unlock combinations I found it would not lock. Took it apart, freed up the arm and I'm back in business again. LUCKY I never lost anything.
Good luck and check the lock /unlock feature too!!

 

[mrjean]

ill check tonight after work. ill lock the car and try to open the liftgate and glass.

as far as my wiper goes, it seems that if the wiper is on the holder it doesnt work, if its out the holder it works fine (albeit i have to put it on 3 start moving but once its active i can put it at 1 and works fine).

the rear defog was working the first day i bought the car, then i open the trunk and glass and it seemed to stop working. sucks in the rain obviously cuz i cant see anythign in the rear. combine that with my faulty front actuators and your in for a fun fun ride with me lol

i just bought the multimeter and has not gotten here yet. however i have never had to use a multimeter and other than a few youtube videos on it, i will be learning tyring to find this issue. can someone help me figure out where to check for ground? and where is the schematic and what am i looking for?

again im so sorry, however when it comes to what wire does what im really basic but willing to learn.

 

[christo829]

ill check tonight after work. ill lock the car and try to open the liftgate and glass.

as far as my wiper goes, it seems that if the wiper is on the holder it doesnt work, if its out the holder it works fine (albeit i have to put it on 3 start moving but once its active i can put it at 1 and works fine).

the rear defog was working the first day i bought the car, then i open the trunk and glass and it seemed to stop working. sucks in the rain obviously cuz i cant see anythign in the rear. combine that with my faulty front actuators and your in for a fun fun ride with me lol

i just bought the multimeter and has not gotten here yet. however i have never had to use a multimeter and other than a few youtube videos on it, i will be learning tyring to find this issue. can someone help me figure out where to check for ground? and where is the schematic and what am i looking for?

again im so sorry, however when it comes to what wire does what im really basic but willing to learn.

Mooseman has a lot of the manuals here:

http://gmtnation.com/f23/need-service-manuals-get-them-here-371/

You can dig through the 2002-2005 volume and get the diagrams you need from there.

There's also specific threads that show the ground locations here on GMTN, but thanks to the way the office has
IE set up, I'm having trouble getting to them from here. Just search for ground locations...it'll come up.

Cheers-

Chris

 

[sawicksted]

ill check tonight after work. ill lock the car and try to open the liftgate and glass.

as far as my wiper goes, it seems that if the wiper is on the holder it doesnt work, if its out the holder it works fine (albeit i have to put it on 3 start moving but once its active i can put it at 1 and works fine).

the rear defog was working the first day i bought the car, then i open the trunk and glass and it seemed to stop working. sucks in the rain obviously cuz i cant see anythign in the rear. combine that with my faulty front actuators and your in for a fun fun ride with me lol

i just bought the multimeter and has not gotten here yet. however i have never had to use a multimeter and other than a few youtube videos on it, i will be learning tyring to find this issue. can someone help me figure out where to check for ground? and where is the schematic and what am i looking for?

again im so sorry, however when it comes to what wire does what im really basic but willing to learn.

I am not very good with a multimeter either. I used the latch/lock posts on the truck where the lift gate hooks on for my ground with an aligator clip and checked both sides of the grid for power at each end of each line. I did use a longer ground wire to reach where I needed to go.
Good luck.

 

[Venomhatch]

Ok so I realized I am having this issue as well. No Wiper function, no lock or unlock function, I didn't think to check license plate lights. But I checked all three Orange wires in the boot and on the lift gate at the points they have connectors for what ever they plug into all say 14 volt. Even the wiper motor Orange wire. At the top of the hatch, I checked the boot, plug in the hatch behind the boot, the other boot that attaches to the car and not a break anywhere. Not even a questionable scratch or scrape. I guess I have a bad module then? Is that safe to assume? All fuses are good. Any suggestions?

 

[christo829]

Ok so I realized I am having this issue as well. No Wiper function, no lock or unlock function, I didn't think to check license plate lights. But I checked all three Orange wires in the boot and on the lift gate at the points they have connectors for what ever they plug into all say 14 volt. Even the wiper motor Orange wire. At the top of the hatch, I checked the boot, plug in the hatch behind the boot, the other boot that attaches to the car and not a break anywhere. Not even a questionable scratch or scrape. I guess I have a bad module then? Is that safe to assume? All fuses are good. Any suggestions?

Sometimes the wires can be broken and not have a visible break in them (insulation intact). You've checked for voltage. but you still need to verify ground and also the data connections.

Chers-

Chris

 

[Real McCoy]

But I checked all three Orange wires in the boot and on the lift gate at the points they have connectors for what ever they plug into all say 14 volt. Even the wiper motor Orange wire. At the top of the hatch, I checked the boot, plug in the hatch behind the boot, the other boot that attaches to the car and not a break anywhere. Not even a questionable scratch or scrape.

Did you verify the ground wire is good also?

 

[Venomhatch]

Did you verify the ground wire is good also?

I will right now. All locations? including in the harness from the truck to hatch? I checked all wires directly grounding to the liftgate with the meter.

Also I found this module for about 16$ will it work in mine. They say it will and it is brand new.
View attachment 30507

Mine has different part numbers here:
View attachment 30508

 

[Venomhatch]

Sometimes the wires can be broken and not have a visible break in them (insulation intact). You've checked for voltage. but you still need to verify ground and also the data connections.

Chers-

Chris

How do I check the data one?

 

[christo829]

How do I check the data one?

You can check continuity on those wires as well as the ground wiring going from connector to connector, or
by piercing the insulation in the wiring before and after the hinge area (since that's the most likely place
for a break), assuming your probes are sharp enough, or you've got clips and some pins. Does your meter
have a continuity setting, or just resistance?

Also, if you get a brand new module, you'll still have to get it programmed. A used one would
not have to be. Make sure that one didn't come from an XUV. I think it mentions at the beginning of this
thread that they're a slightly different beast.

Cheers-

Chris

 

[mrjean]

ok so updating on my situation...

my glass and trunk both lock when i lock the car with the keyfob
my wiper works fine now on and off the base
my license plate bulbs work fine

took the boot off and the cables seem ok. now onto the pics

View attachment 30509
View attachment 30510
View attachment 30512
View attachment 30511
View attachment 30513

 

[Venomhatch]

You can check continuity on those wires as well as the ground wiring going from connector to connector, or
by piercing the insulation in the wiring before and after the hinge area (since that's the most likely place
for a break), assuming your probes are sharp enough, or you've got clips and some pins. Does your meter
have a continuity setting, or just resistance?

Also, if you get a brand new module, you'll still have to get it programmed. A used one would
not have to be. Make sure that one didn't come from an XUV. I think it mentions at the beginning of this
thread that they're a slightly different beast.

Cheers-

Chris

Updated: I checked continuity in blue, black, and brown wires at boot all are fine.
This is the meter I have currently available.
View attachment 30514

 

[Venomhatch]

So this is what I have found out on the LG Wires:

LCM
View attachment 30520

Wiper Motor/Module
View attachment 30521

 

[mrjean]

where are those pictures located?

 

[Venomhatch]

where are those pictures located?

They are on my liftgate.

 

[mrjean]

i got my multimeter today just wondering how im going to stretch it out from one end to the other.

 

[Venomhatch]

So this is what I have found out on the LG Wires:

LCM
View attachment 17334

Wiper Motor/Module
View attachment 17335

So I still cant find where the problem is. Also I have checked ground on all tailgate wires (see pics). Signal wire, Brown wire, and all other wires in boot all read like there is no broken connections and with the ignition off.

*** Why does the LCM need to get reprogrammed if I go and get a brand new one on ebay? Can it be done with a DIY here?

 

[misterhyde]

*** Why does the LCM need to get reprogrammed if I go and get a brand new one on ebay? Can it be done with a DIY here?

I too would like to know the reprogamming entails? Is it just for the Keyless system cause anyone can do that. I might have a bad board as well and would like to replace it with a used.

 

[The_Roadie]

GM makes SURE their modules aren't plug and play like USB peripherals, to make sure the dealers can scrape $$ off people after the warranty runs out. In the case of the LGM, I'm guessing (with no insider details) that the "reprogramming" consists only of configuring whether or not the vehicle even had remote entry. I think some rental fleet vehicles had no remote entry option installed, so the BCM and perhaps the LGM would have to be told that. It could also be that the virgin LGMs that were never installed by a dealer or the factory just have some blank flash memory that the comm protocols need to be installed into as firmware. GM might have done this in case the firmware ever needed to be updated in the future on their dime, since a data bus update is cheaper than having to swap out the modules and send them into a depot for reprogramming.

Can you imagine GM ever giving up the revenue stream of firmware updates by offering them as USB-cable updates? Or bluetooth Smartphone updates? Never happen.

 

[Venomhatch]

GM makes SURE their modules aren't plug and play like USB peripherals, to make sure the dealers can scrape $$ off people after the warranty runs out. In the case of the LGM, I'm guessing (with no insider details) that the "reprogramming" consists only of configuring whether or not the vehicle even had remote entry. I think some rental fleet vehicles had no remote entry option installed, so the BCM and perhaps the LGM would have to be told that. It could also be that the virgin LGMs that were never installed by a dealer or the factory just have some blank flash memory that the comm protocols need to be installed into as firmware. GM might have done this in case the firmware ever needed to be updated in the future on their dime, since a data bus update is cheaper than having to swap out the modules and send them into a depot for reprogramming.

Can you imagine GM ever giving up the revenue stream of firmware updates by offering them as USB-cable updates? Or bluetooth Smartphone updates? Never happen.

Yes, Since my question on this it has to come from another TB that has or had keyless in that one also. Once you plug it in, it is just the programming your transmitters to it.

 

[triz]

Stupid question but did you pull the actual latch to make sure the module that pulls is not broken? Mine was busted in half.

 

[Venomhatch]

Stupid question but did you pull the actual latch to make sure the module that pulls is not broken? Mine was busted in half.

Yeah I am locking the latch manually and pulling a small string I have hidden to unlock it manually.