Liftgate Control Module

[mrjean]

hello guys,
i have an update on my rear defogger/wiper situation.

1. i was at the shop and decided to take a look at the lgm. since i knew for a fact that the rear defogger was working at one point, i knew it was not the grid. and SO, at the shop we but the volt on the connectors at the grid and they didnt work...he put the volt on the wires (the left most black connector on the lgm from the pics in this thread) and after he "zaped" it with positive/negative check, the grid started defogging/working again when i pressed the rear defog button in the front. however, after opening the liftgate/glass a few times, stopped working (im not sure if opening the tailgate and glass is actually affecting anything at the lgm or the wiper module/motor). my license plate bulbs and keyfob lock unlock at the lift gate have never stopped working once. they have always worked perfect.

2. REAR WIPER... we really didnt check the wiper motor OR the white module sitting on top of it, only the lgm (and after the "zap" above, my wiper worked flawlessly for the same time my defogger worked). however here is the issue i have with it. intermittently it will stop working. when i have it to 1, 2 or 3 it works when it wants. sometimes it works all the time, sometimes it doesnt work at all. sometimes, ill have it on and it works for a bit and then "freezes" on the on position. i switch it to zero or off and wiper stays stuck as if it was on. THEN all of a sudden it will wipe how ever many times it would of wiped for the amount of time i had it turned on. its the oddest thing. also, whether the wiper reacts tot he 1, 2 or 3 position on the switch, it ALWAYS shoots water out i can see it on my rear view mirror.

**now, here is what i dont know if its causing an issue...my mode and what i beleive to be the defrost actuator, are bad. so the air is not circulating correctly. would excessive heat/cold cause the switch at my knee to not send the signal to the wiper? or send it late?

 

[misterhyde]

I had no power getting through the defroster strips on the rear glass. At first I found a few freyed power wires hidden in the hinge boot. But that did not solve the problem. Then after buying a salvaged/used LGM and still not solving the problem, I inspected every wire as much as I could. Found that the large orange power wire at the LGM was pulled out from the connector more than the others (more copper wire exposed). So I pulled the 4 or 5 wires out of the connector and found that the larger orange wire was also freyed at the pin fitting. So I pulled it apart, restripped the wire, and also soldiered it. This solved my problems.

 

[xtitan1]

I had no power getting through the defroster strips on the rear glass. At first I found a few freyed power wires hidden in the hinge boot. But that did not solve the problem. Then after buying a salvaged/used LGM and still not solving the problem, I inspected every wire as much as I could. Found that the large orange power wire at the LGM was pulled out from the connector more than the others (more copper wire exposed). So I pulled the 4 or 5 wires out of the connector and found that the larger orange wire was also freyed at the pin fitting. So I pulled it apart, restripped the wire, and also soldiered it. This solved my problems.

Wow that's intense. I thought I was the only one who would spend hours trying to fix small things like that. It's very cathartic to know there's a whole bunch of like minded guys out there. It seems like a common trait of gmt nation members. Then again, I'm not really sure how to even turn the rear defroster on in the first place!

 

[Venomhatch]

I had no power getting through the defroster strips on the rear glass. At first I found a few freyed power wires hidden in the hinge boot. But that did not solve the problem. Then after buying a salvaged/used LGM and still not solving the problem, I inspected every wire as much as I could. Found that the large orange power wire at the LGM was pulled out from the connector more than the others (more copper wire exposed). So I pulled the 4 or 5 wires out of the connector and found that the larger orange wire was also freyed at the pin fitting. So I pulled it apart, restripped the wire, and also soldiered it. This solved my problems.

I think I will take another look at it today. Thank you.

 

[The_Roadie]

...after he "zaped" it with positive/negative check, the grid started defogging/working again

Meters don't work that way. The ONLY thing that happened that could affect operation of the circuits is that touching them with the meter could move them and cause an open connection to touch and start working because of the mechanical movement. It hints to me that you have a loose/oxidized/dirty connection in there.

when i pressed the rear defog button in the front. however, after opening the liftgate/glass a few times, stopped working (im not sure if opening the tailgate and glass is actually affecting anything at the lgm or the wiper module/motor).

Again, mechanical motion of the bumping caused by the glass. Makes an intermittent connection work and not work. Nothing will fix it permanently other than locating where the issue is (by wiggling wires) and then repair the root cause. Wires are often broken inside the insulation.

**now, here is what i dont know if its causing an issue...my mode and what i beleive to be the defrost actuator, are bad. so the air is not circulating correctly. would excessive heat/cold cause the switch at my knee to not send the signal to the wiper? or send it late?

Auto components are designed for normal environmental extremes, from -40 to +150F.

 

[mrjean]

Meters don't work that way. The ONLY thing that happened that could affect operation of the circuits is that touching them with the meter could move them and cause an open connection to touch and start working because of the mechanical movement. It hints to me that you have a loose/oxidized/dirty connection in there. Again, mechanical motion of the bumping caused by the glass. Makes an intermittent connection work and not work. Nothing will fix it permanently other than locating where the issue is (by wiggling wires) and then repair the root cause. Wires are often broken inside the insulation. Auto components are designed for normal environmental extremes, from -40 to +150F.

and this mr the roadie, is why you are the man. ill take another look at the connection. i was ready to buy a new lgm on ebay for 15 bucks (then i remember that i needed to have it programmed at the dealer).

one thing that boggles my mind is this...if it is a cable issue and not a LGM issue, would that cause my wiper to work intermittently? more importantly, will the lgm "remember" the number of wipes that the wiper did not do while it was on and stuck on the "on" position once i turn it off? because i have to tell you, i get a kick of it everytime it does it. ill have it on 1 and the wiper will be on the on possition but do nothing, i forget i have it one for like 10 minutes and then i turn it off once i see its not working, it then (a few minutes later), go on to wipe the equivalent amount of wipes it should have done in that time frame.

 

[rwoodruff1]

I have also been fighting a bad rear wiper motor on an '03 trailblazer. I found a broken orange wire in the wire boot, which I fixed. The rear wiper still does not work. Question - does the motor need to be mounted in place to work (so it is grounded)? I found a used motor at the junk yard and plugged it in w/o mounting it and it did not work. I got to thinking afterward that maybe it needs to be grounded??? thanks for any info on this topic

 

[David B.]

I've been following along with the LGM threads, since I've lost the use of my Key Fobs. I was hoping for a simple broken wire in the transition from the interior of the TB to the Tailgate, but they're intact. My specific question is this- I put the TB in programming mode following the forum instructions after replacing the battery on my Fob in order to program my Fob to the LGM. When following the instructions, the locks cycled while holding down the Fob buttons just as they should to signal that they're in sync with the LGM. But after exiting programming mode and testing the Fob, no luck. They're still not working. If there was a problem with the LGM or the wires leading to it, wouldn't be unable to recognize that I'm trying to program a Fob to it? I'm thoroughly confused lol

 

[David B.]

Quick update, was able to confirm that both my Key Fobs have the exact same reaction to reprogramming, and both have brand new batteries. They both seem to take to reprogramming by triggering the locks after about 15 seconds, but then they still will not function to lock or unlock the doors when I exit the TB out of programming mode.

 

[budwich]

are you sure that your locks are cycling and going thru unlock and lock sequences?

 

[David B.]

During the reprogramming mode, while holding down both the unlock/lock buttons on my fobs, the locks in the TB definitely cycle "lock then unlock" one time, then I'm letting go of the buttons and the fob and turning the ignition to "on" then back to "off", cycling the locks again without me touching anything and honking the horn. But after that, the fob still won't work to lock/unlock

 

[Venomhatch]

During the reprogramming mode, while holding down both the unlock/lock buttons on my fobs, the locks in the TB definitely cycle "lock then unlock" one time, then I'm letting go of the buttons and the fob and turning the ignition to "on" then back to "off", cycling the locks again without me touching anything and honking the horn. But after that, the fob still won't work to lock/unlock

That's the same boat I am in. It recognizes the fob but doesn't keep the programming. I noticed though my rear wiper doesn't work and the liftgate doesn't lock and unlock on its own with the fob either.

 

[David B.]

Well my rear wiper worked, as well as licens plate lights and rear hatch function. However, $85 for a used 2005 LCM and a quick program and both my fobs now function. I kind of figured it was the LCM since I traced EVERYTHING else lol. Hopefully the repair sticks

 

[Venomhatch]

Well my rear wiper worked, as well as licens plate lights and rear hatch function. However, $85 for a used 2005 LCM and a quick program and both my fobs now function. I kind of figured it was the LCM since I traced EVERYTHING else lol. Hopefully the repair sticks

Mine:
Wiper: Not Working
License Lights: Working
Rear Defrost: Not Working
Keyless: Not Working and wont program either.
Liftgate: Wont Lock or Unlock via Key FOB.

*And yes mine came with Keyless Option!

 

[David B.]

Venomhatch, yours definitely sounds like a broken loose wire/wires, especially ground since the license plate lights aren't working.

 

[Venomhatch]

Venomhatch, yours definitely sounds like a broken loose wire/wires, especially ground since the license plate lights aren't working.

The license plate lights are working!

 

[David B.]

Haha sorry, I see that now. I suspect an orange wire

 

[jsheahawk]

Heya, guys.

I'm trying to narrow down my liftgate issues. I noticed the rear defogger went from working, then only a few lines worked, then it died. Shortly after that, the rear wiper stopped working. When the wiper stopped working, I noticed the gate wasn't locking. I don't know when that started happening.

My evidence:
- 12V on both orange wires of the plug under the boot (measured against the black ground wire there)
- I only have two orange wires there. One is thicker than the other. Roadie mentioned there were three orange wires, and I searched for a third, but it must be a 2002 LT/short wheel base thing.
- 12V across both orange wires at the LGM (measured against the black ground wire at that plug)
- 12V on the orange wire at the wiper motor (measured against the black ground wire there)
- No voltage potential across the defogger grid
- The rear washer isn't working. I'm thinking this must be a separate problem since it's not controlled by the LGM.
- I pulled the switch from the dash, and I think the washer is controlled by pins 1 and 5. There is continuity across those pins when I press the washer button but not when it isn't pressed.
- Closing and opening the gate cycles the gate's lock
- The unlock/lock buttons don't lock/unlock the gate
- I don't have keyless entry

So what else do I need to do check to narrow it down to the LGM (or not)? I've read that it's usually a broken wire, but I can't track one down.

I should note that all of these measurements were done with the gate open. Thanks, guys.

Jared

 

[The_Roadie]

The typical thing that kills LGM functions assuming it has power is the data communication wire in the hinge area. And some things like the wiper are suppressed when the liftgate is open anyway.

 

[jsheahawk]

The typical thing that kills LGM functions assuming it has power is the data communication wire in the hinge area. And some things like the wiper are suppressed when the liftgate is open anyway.

Thanks for the quick reply, Roadie.

View attachment 32635

So the two oranges are 12V and black is ground. Is brown (or is that violet...) or blue data? And what is the other? I have downloaded the wiring diagrams, but I have to admit that as decently handy as I fancy myself, they are a bit out of my depth.

Do I just test continuity on the data line to check for fault?

Jared

 

[The_Roadie]

I think it's blue. A search might locate one of the other threads it's been discussed in. Sorry, in a bit of a rush this morning.

 

[jsheahawk]

I think it's blue. A search might locate one of the other threads it's been discussed in. Sorry, in a bit of a rush this morning.

No worries, Bill. You are pretty much "the Trail-voy-scender guy". Getting a reply is enough.

I'll check it and reply back.

Jared

 

[Real McCoy]

Yes, the Blue is the data line. I believe that the brown is for the license plate lights.

Doug

 

[jsheahawk]

Yes, the Blue is the data line. I believe that the brown is for the license plate lights.

Doug

Excellent. I'll check it for continuity tonight. Thanks, McCoy.

Jared

 

[jsheahawk]

So no continuity on the data line between the plug at the hatch and the splice pack under the back seat.

I dig further into the boot and find:
View attachment 32662

So this is my apology:
I am sorry for doubting the community at large, and Roadie and McCoy specifically. I should have known better than to think that I was unique and had a problem that hadn't been solved a million times on this forum. In the future, I promise to listen more closely to your sage advice. I can't promise it won't happen again, but I assure you that I'll work on it!

That said, the rear wiper still isn't working. I'll check continuity on all of the wires going to it tomorrow. One odd thing is that the rear washer started working when I fixed the wire breaks. I was under the impression that the washer was a completely different circuit. Weird.

Jared

 

[The_Roadie]

Thanks for the report the the kind words about the folks here on the forum.

The washer *is* entirely separate. But it and the rear wiper functions may be suppressed if the LGM thinks the liftgate or liftglass is not latched. That may be corrosion or high friction in the switch mechanism down near the latch. Some members have reported penetrating oil can free those up. When you use the keyfob to lock the truck, do both the liftgate and the glass lock?

Or you could have another wiring problem or fault involving the wiper motor.

 

[jsheahawk]

Thanks for the report the the kind words about the folks here on the forum.

The washer *is* entirely separate. But it and the rear wiper functions may be suppressed if the LGM thinks the liftgate or liftglass is not latched. That may be corrosion or high friction in the switch mechanism down near the latch. Some members have reported penetrating oil can free those up. When you use the keyfob to lock the truck, do both the liftgate and the glass lock?

Or you could have another wiring problem or fault involving the wiper motor.

I'll try penetrating oil to see if that helps.

I have the LS, so no keyless entry. On that note: Is the LGM what is programmed with whether or not a TB has keyless entry, or is that held in the PCM or BCM? Thus, can I swap LGMs to gain keyless entry? I'd have to guess no.

Jared

 

[Real McCoy]

Jared,
I have an LS and it has keyless entry - I am pretty sure it was standard on all models. I am guessing you bought the TB used and perhaps the key fobs were lost before your purchase.
Doug

 

[jsheahawk]

Jared,
I have an LS and it has keyless entry - I am pretty sure it was standard on all models. I am guessing you bought the TB used and perhaps the key fobs were lost before your purchase.
Doug

Nope. No AU0 in the glove box, and I have a key cylinder on the passenger side. I've read that all of the hardware is there, but it's just a software switch that is either set to on (yay!) or off (damnit!). That's why I'm wondering where that software setting is stored. If it's stored in the LGM then -- theoretically -- I'd be able to swap out my LGM for a wrecked truck with keyless entry's LGM and have it. I bet it's not that easy. Can anyone advise?

Jared

 

[dla442]

I had my remote key, the tailgate lock etc fail. Nought I did all the checks but kissed the small gage wire in the wire bundle on top of the lift gate. Nought a new lgm and found out the hard way. Anyway, the wire was broken. I have a programmed lgm that's out of a 2005 lt2 trailblazer if anyone wants to buy it. I tested the orange wires too...but missed one. Funny though..the license plate light worked!

 

[IllogicTC]

I had my remote key, the tailgate lock etc fail. Nought I did all the checks but kissed the small gage wire in the wire bundle on top of the lift gate. Nought a new lgm and found out the hard way. Anyway, the wire was broken. I have a programmed lgm that's out of a 2005 lt2 trailblazer if anyone wants to buy it. I tested the orange wires too...but missed one. Funny though..the license plate light worked!

The Body Control Module has command of the exterior lighting relay, and the wires run for the most part directly to their lamps (or boards that control lamps, like the tail lights). For the license lamps, there's a brown wire running off Fuse 14 in the rear fuse block that feeds power directly to the lamps.

 

[Venomhatch]

I had my remote key, the tailgate lock etc fail. Nought I did all the checks but kissed the small gage wire in the wire bundle on top of the lift gate. Nought a new lgm and found out the hard way. Anyway, the wire was broken. I have a programmed lgm that's out of a 2005 lt2 trailblazer if anyone wants to buy it. I tested the orange wires too...but missed one. Funny though..the license plate light worked!

That is exactly how mine is. License lights work fine. But nothing else functions!

 

[dla442]

That is exactly how mine is. License lights work fine. But nothing else functions!

the orange wire that the module uses for communication was the one the had broken on our TB. Hence why my new module would not program until it was repaired..so i have an extra module now. lessons learned for not being thorough enough with checking ALL the orange wires. ahaha

 

[The_Roadie]

Orange wires back there are 12 V power, IIRC, but glad you found the fault!

 

[Venomhatch]

I had my remote key, the tailgate lock etc fail. Nought I did all the checks but kissed the small gage wire in the wire bundle on top of the lift gate. Nought a new lgm and found out the hard way. Anyway, the wire was broken. I have a programmed lgm that's out of a 2005 lt2 trailblazer if anyone wants to buy it. I tested the orange wires too...but missed one. Funny though..the license plate light worked!

Do you still have this liftgate module I'm about to private message you about it.

 

[0u812]

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.

All the same issues, but also a strange sound as though the liftgate locks were locking and unlocking at what seemed to be half the sound strength as normal. I removed the boot, found the black wire had broken completely. I ran a new wire through the boot, spliced in the new piece, sealed it with a color coded heat shrink coating. Then the lock was sounding full strength, however it was working in reverse and the key fobs were still not working. Obviously I had missed something. I removed the boot on both sides. I then grabbed each wire one at a time from either side of the boot and pulled. The blue (small) wire was also completely broken. I spliced and shrink wrapped in another wire. This time, all good. Rear defog, license plate lights, rear wiper, rear liftgate lock and key fobs all working. Would I have been able to solve this without everyone's input from this site? Yes... eventually... it is who I am to keep looking. Could I have solved it in 5 minutes? No.... in fact I would probably have started at the fuse box and started tracing the wires to test continuity... I would have been out there for hours.

Thanks Guys. Keep up the great work... It matters.

 

[jsheahawk]

All the same issues, but also a strange sound as though the liftgate locks were locking and unlocking at what seemed to be half the sound strength as normal. I removed the boot, found the black wire had broken completely. I ran a new wire through the boot, spliced in the new piece, sealed it with a color coded heat shrink coating. Then the lock was sounding full strength, however it was working in reverse and the key fobs were still not working. Obviously I had missed something. I removed the boot on both sides. I then grabbed each wire one at a time from either side of the boot and pulled. The blue (small) wire was also completely broken. I spliced and shrink wrapped in another wire. This time, all good. Rear defog, license plate lights, rear wiper, rear liftgate lock and key fobs all working. Would I have been able to solve this without everyone's input from this site? Yes... eventually... it is who I am to keep looking. Could I have solved it in 5 minutes? No.... in fact I would probably have started at the fuse box and started tracing the wires to test continuity... I would have been out there for hours.

Thanks Guys. Keep up the great work... It matters.

Nice! Isn't the amount of knowledge floating around this site amazing?

Jared

 

[jsheahawk]

That said, the rear wiper still isn't working. I'll check continuity on all of the wires going to it tomorrow. One odd thing is that the rear washer started working when I fixed the wire breaks. I was under the impression that the washer was a completely different circuit. Weird.

Jared

Turns out that me fiddling with the wires in the boot blew the LGM fuse. I know for a fact that it was good before I started diagnosing. All problems solved! The LGM fuse runs the rear wiper and the defogger.

Jared

 

[dla442]

I Have a lgm if you still still need one. From a 05 lt2 TB.

 

[jsheahawk]

I Have a lgm if you still still need one. From a 05 lt2 TB.

Nah...I think I'm good.

Jared