I need a little help here. It appears that the module that controls the lic. plate lights, rear wiper, and tailgate lock/unlock is fried. Or atleast I am guessing it is not performing any of the following functions, and when I do something like turn on the rear wiper it just clicks. With that being said I need a new one ASAP, with that comes two questions, does the new module need to be flashed, and is this module the one that controls the FOB remotes?
Lift Gate Control Module
- Thread starter andy702252
- Start date
AtlWrk
Member
- Dec 6, 2011
- 674
Have you thoroughly inspected the wiring inside the rubber boot at the top of the liftgate? There have been several reports from members who have had wires crack in that location since it gets flexed so much. My money is on that rather than a dead module. And yes, the liftgate module (LGM) is the receiver for the remote key fobs.
I am having similar issues with either wiring to and from the LCM (Rear Body Control Module or Liftgate Control Module, whichever you prefer), the LCM itself or the BCM. I have a 2002 Envoy. I do know that if you buy a new module that it has to be dealer programmed. If you can find a used working module, it should be plug and play. Or, if you know anyone with your vehicle, buy some beer and ask to do a swap to see if it is indeed the module that has gone bad. I would try to find a module from the same year as your vehicle as I do not know if later year modules will work in older vehicles. Also, verify that wires in the rubber boot between the liftgate and body are not cracked or broken as that can cause problems with accessory functionality and is a very, very common problem with our trucks do to the constant opening and shutting of the liftgate.
If anyone has any insight to my problem, it would be helpful. All equipment at the liftgate works, lights, locks, RKE, defogger. I have a 2 amp draw on the battery constantly with the engine off. IPC/DIC pulls .43 amps. Radio pulls 1 amp. HVAC .12 amps. and a few other minor draw on other modules. Fuse #6 under in the rear fuse block is one of two that control the LCM. When that fuse is pulled the draw from other those items is dissappears. Of course the instrument panel and radio are drawing full power but are not actually on which leads me to think that the LCM is bad. The constant draw isn't intermittent. Does this sound like the LCM or more like the BCM? If it was wiring I would think I would loose functionality with some features. I did inspect the wiring at the boot and found nothing. Continuity and voltage seem to be good.
RayVoy
Member
- Nov 20, 2011
- 939
Are you saying, if you pull fuse #6 all parasitic drains are gone?macinnis17 said:
Can you explain how you reached this conclusion?macinnis17 said:
Most are not.macinnis17 said:
Could we have a MOD split this thread so we can deal with the two problems separately.what fuses are you getting your readings from for your drains? what radio setup do you have? Steering controls???? rear seat controls?
Wasn't trying to take this thread over and turn it into two separate issues. There are almost no past threads that describe vehicle symptoms like mine so I commented on the initial issue, thought maybe explain mine also, and see if anyone had any insight. Have read so many different posts about the Rear Body Control Module and almost all are frayed or broken wiring at the liftgate hinge. Some are rear windshield wiper. Very few actually have a bad module. I will start a new thread.
I know you guys know far more than I do, but you said check the wires at the top. Its making a clicking sound, it wouldnt make the clicking sound if it wasnt not getting power right?
in your case, are your locks working... you didn't indicate this. Further, I do believe the "check the wires" applies whether your module is receiving power or not, cause there are other wires also. If they are broken, then those functions won't work regardless of whether there is "clicking" or not.
AtlWrk
Member
- Dec 6, 2011
- 674
andy702252 said:
It depends. A big clue is that your license plate lights do not work, correct? They are not controlled by the LGM but they do share a common ground that runs through that rubber boot to a ground at the pillar in the rear hatch area.
Turn on your parking lights. Does this stop the clicking?
AtlWrk
Member
- Dec 6, 2011
- 674
I drew up some schematics to show you what I'm getting at.
The blue box represents what is inside the liftgate. When the ground wire in the boot breaks (second picture) the license plate bulbs and the liftgate lose their ground to the vehicle but are still connected to each other. When the license plate and parking lights aren't on they provide an alternate indirect ground path as shown. Because you're going through two light bulbs you can't get enough current to actually power the wiper motor or locks--but you can get some clicks and whatnot from them. All that being said it is possible that your LGM has failed, but it's a helluva lot easier and cheaper to fix a broken wire.
The blue box represents what is inside the liftgate. When the ground wire in the boot breaks (second picture) the license plate bulbs and the liftgate lose their ground to the vehicle but are still connected to each other. When the license plate and parking lights aren't on they provide an alternate indirect ground path as shown. Because you're going through two light bulbs you can't get enough current to actually power the wiper motor or locks--but you can get some clicks and whatnot from them. All that being said it is possible that your LGM has failed, but it's a helluva lot easier and cheaper to fix a broken wire.
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Denali n DOO
Member
- May 22, 2012
- 5,596
I just wanted to add that I too have had the same issue as you. http://gmtnation.com/f23/liftgate-problems-dealer-says-3526/. I checked the wires in the boot and found no issues with them, even tugged good n hard on them all. Then I took to the dealer to diagnose, GM Tech said new LGM and new latch required, about $1000. I then came back to this site asked more questions and was lead back to the rubber boot. It takes a lot of messing around to inspect the entire length of wire under the boot. Even though I thought I checked mine really good the first time, my second inspection revealed a broken black and cracked orange wire, nothing wrong with my LGM or latch as GM said. If you ruin the rubber boot while looking around I'll be happy to send you my extra boot. Vaseline inside the boot will help you slide the wires and boot around in there, its really tight and I think I had to unplug a connection on the body side to get enough room to see them all. Check the wires again if you can. I have a LGM here too that I took of a TB that was heading to the wreckers. If your LGM turns out to be the problem It'll send you my extra LGM free of charge. If you take me up on the parts all I ask is that you cover the shipping costs.
The common ground mentioned in post above is inside the cargo area driver side near the lift gate bump stop under the panel, the panel has slots in it that you can the the ground bolt.
The common ground mentioned in post above is inside the cargo area driver side near the lift gate bump stop under the panel, the panel has slots in it that you can the the ground bolt.
AtlWrk
Member
- Dec 6, 2011
- 674
RayVoy said:
The LGM isn't grounded to the liftgate. You'll have to splice into the black wire that runs to the four pin connector of the LGM, run that up and through the boot and then ground somewhere on the body. The ground under the trim next to the liftgate bump stop is probably the easiest. You'll have to take off a few pieces of trim.
RayVoy
Member
- Nov 20, 2011
- 939
Ok, I'm not going to get into a "pissing match" with you. I no longer have my manuals and I had no reason to remove the interior panels on my lift-gate. However, I would be very surprised to find the sheet metal of the lift-gate is not at ground potential. Every piece of metal on every vehicle that I have ever worked on was grounded.AtlWrk said:
AtlWrk
Member
- Dec 6, 2011
- 674
No pissing match intended. I'm sure the lift gate is at ground potential from its physical connection through the hinges etc. I'm not arguing that. All I'm saying is that the LGM is not grounded to the liftgate sheetmetal. It only has a direct connection back to the body--which in the OP's case is broken. Connecting a body stud to a liftgate stud won't fix this as the LGMs ground wire still won't be connected to anything.
RayVoy
Member
- Nov 20, 2011
- 939
This may be so, the module may not be grounded. However, the OP responded with the following, when you asked about the lights:AtlWrk said:
No lights is a sheetmetal ground problem.andy702252 said:
This may be be broken, however, we do know that the lights do not work. My suggestion is to fix the ground for the lights first, if indeed the module still does not work after the lights are fixed, tackle the module ground after the sheetmetal ground.AtlWrk said:
AtlWrk
Member
- Dec 6, 2011
- 674
Ahh, I gotcha. It's not clear from the diagrams but the LGM, lights and rear defroster grounds splice together (S901) before running through the boot and back to the body on a common ground to G401. If the ground wire cracks in the boot (between the ground and splice) you lose all of those components. That's why I asked about the lights.