Liftgate Control Module

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
I recently bought a 2005 TrailBlazer and the rear wiper doesnt work, rear licence plate lights, and key fob doesnt work (havent had chance to see if rear defroster is working). After some searching online I found it is common for the wires to break where they bend into the rear door, after a visual inspection all seem good, but once I get time I will test the resisitance with a multi-meter, to be positive.
Now if all wires are good it seems that this leads to a bad LCM? The rear door still unlocks and opens without an issue. Is there anyway to test the LCM unit itself with a multi-meter to determine if it is good or not? Is there any reprogramming that will need to be done if I replace the unit? (I will most likely pick one up from local salvage yard)
Thanks
 

6716

Member
Jul 24, 2012
830
DirtRidinZ71 said:
Now if all wires are good ....

Have fun in there. I've been futzing with the LCM and locking mechanism on and off for months and months. Still haven't figured it out.

Plenty of folks around here are better at that kind of stuff than I am, though.

Don't know if you tried this, but double check it's not the bulbs for the plate light. I've had to replace both.
 

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
6716 said:
Don't know if you tried this, but double check it's not the bulbs for the plate light. I've had to replace both.

Thanks, I have not had the chance to check out the light bulbs yet, will be first thing I do when I get another chance at it. Only had it a week so far.
 

Denali n DOO

Member
May 22, 2012
5,596
DirtRidinZ71 said:
I recently bought a 2005 TrailBlazer and the rear wiper doesnt work, rear licence plate lights, and key fob doesnt work (havent had chance to see if rear defroster is working). After some searching online I found it is common for the wires to break where they bend into the rear door, after a visual inspection all seem good, but once I get time I will test the resisitance with a multi-meter, to be positive.
Now if all wires are good it seems that this leads to a bad LCM? The rear door still unlocks and opens without an issue. Is there anyway to test the LCM unit itself with a multi-meter to determine if it is good or not? Is there any reprogramming that will need to be done if I replace the unit? (I will most likely pick one up from local salvage yard)
Thanks

All the same symptoms as mine had. Dealer quoted $760 for new module and latch :rotfl:. I looked at the wires in the boot and they looked fine but I went back at it a second time and moved the boot as far up the wires as I could and pulled the broken black wire out, they are tight in the boot and hard to really see. I used Vaseline to slide the wire back through the boot and did a repair solder and shrink tube. http://gmtnation.com/f23/liftgate-problems-dealer-says-3526/ , maybe revisit the boot again.

Oh, and welcome to GMTNation...
 

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
Denali n DOO said:
All the same symptoms as mine had. Dealer quoted $760 for new module and latch :rotfl:. I looked at the wires in the boot and they looked fine but I went back at it a second time and moved the boot as far up the wires as I could and pulled the broken black wire out, they are tight in the boot and hard to really see. I used Vaseline to slide the wire back through the boot and did a repair solder and shrink tube. http://gmtnation.com/f23/liftgate-problems-dealer-says-3526/ , maybe revisit the boot again.

Oh, and welcome to GMTNation...

Thanks for the welcome. Your post is one of the ones I came across in my searching. Hopefully the weather will be nice this weekend and I can check out the wires better and test for resistance. I will do that before dropping any money for a new LCM.
 

RayVoy

Member
Nov 20, 2011
939
As Denali suggests, the problem is probably a broken ground wire in the boot.

To test, just connect a temp jumper between a good ground point on the gate and a good ground point on the body. This will provide a bypass for the broken ground wire and should provide the necessary ground circuit.

If everything works, you have a broken ground wire.
 

Gevans17

Member
Jan 8, 2012
63
RayVoy said:
As Denali suggests, the problem is probably a broken ground wire in the boot.

To test, just connect a temp jumper between a good ground point on the gate and a good ground point on the body. This will provide a bypass for the broken ground wire and should provide the necessary ground circuit.

If everything works, you have a broken ground wire.

check for 12 volts at the LGM module inside the rear hatch between orange and black wires. You can open the LGM and check for broken solder joints on the circuit board. If LGM is bad, buy a USED one off E-bay. Used ones are plug and play., while new LGMs need to be programmed by your friendly Chevy stealer.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Denali n DOO said:
...Dealer quoted $760 for new module and latch .... tight ... booty ...I used Vaseline ...
There, I edited your thoughts. :rotfl:
 

Denali n DOO

Member
May 22, 2012
5,596
the roadie said:
There, I edited your thoughts. :rotfl:

Ha ha, I been screwed by the dealer so many times that Vaseline is no longer required :rotfl:
 

Gevans17

Member
Jan 8, 2012
63
Denali n DOO said:
Ha ha, I been screwed by the dealer so many times that Vaseline is no longer required :rotfl:

Screw the dealer. Used one is $35-45 on ebay and no programming required. Do not confuse LGm with a BCM body control module :thumbsup:
 

Denali n DOO

Member
May 22, 2012
5,596
Gevans17 said:
Screw the dealer. Used one is $35-45 on ebay and no programming required. Do not confuse LGm with a BCM body control module :thumbsup:

Lol, I did screw the dealer, I fixed mine myself with a bit of solder and shrink wrap, then went back to the dealer and had the $123.00 refunded for the misdiagnosis :thumbsup:, the whole story is in my lift gate thread...
 

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
Well I spent some time with the multimeter tonight and all wires are good, I've got constant 12 volts at the LCM, and wiper motor through the 3 orange wires, ground was tested with continuity and the licence plate lights have power, just burnt bulbs.
Now the blue wire for the motor speed signal always shows 0.30-0.50V with the switch in any of the positions, including off. I have 12V at the switch in the dash but I havent traced it further through the truck to the BCM, will try that tomorrow.
So does it sound like the LCM is working properly and I just have to seperate issues, the rear wiper and the remote entry/start? Anyone know what voltage the speed signal wire for the rear wiper should read? Possiblly just the switch that is bad (if all other wiring is good)?
Thanks
 

Darkrider_LS

Member
Jan 25, 2013
9,332
Welcome over to the Nation man. This is Darkrider from GMT400. Not sure what to suggest on this but def gonna keep tabs on this thread in case this problem ever crops up in my TB.
 

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
Darkrider_LS said:
Welcome over to the Nation man. This is Darkrider from GMT400. Not sure what to suggest on this but def gonna keep tabs on this thread in case this problem ever crops up in my TB.

Thanks, Nice seeing a familiar name here too.

Any other thoughts/opinions on the problem?
 

Darkrider_LS

Member
Jan 25, 2013
9,332
DirtRidinZ71 said:
Thanks, Nice seeing a familiar name here too.

Any other thoughts/opinions on the problem?

Def sounds like you may have two separate issues with the the keyless entry/wipers. I would suggest replacing the rear wiper switch first to see if that helps with the wiper.
 

Black_tb

Member
Dec 6, 2011
817
Darkrider_LS said:
Def sounds like you may have two separate issues with the the keyless entry/wipers. I would suggest replacing the rear wiper switch first to see if that helps with the wiper.


just curious why wouldn't you do simple and free electrical test instead of just throwing money at parts he may or may not need?:confused:
 

Darkrider_LS

Member
Jan 25, 2013
9,332
Black_tb said:
just curious why wouldn't you do simple and free electrical test instead of just throwing money at parts he may or may not need?:confused:

From what i seen it looked like he already did the testing...though granted he may not have tested at the switch.
 

Black_tb

Member
Dec 6, 2011
817
But others have stated that its hard to find usually
 

Gevans17

Member
Jan 8, 2012
63
DirtRidinZ71 said:
Well I spent some time with the multimeter tonight and all wires are good, I've got constant 12 volts at the LCM, and wiper motor through the 3 orange wires, ground was tested with continuity and the licence plate lights have power, just burnt bulbs.
Now the blue wire for the motor speed signal always shows 0.30-0.50V with the switch in any of the positions, including off. I have 12V at the switch in the dash but I havent traced it further through the truck to the BCM, will try that tomorrow.
So does it sound like the LCM is working properly and I just have to seperate issues, the rear wiper and the remote entry/start? Anyone know what voltage the speed signal wire for the rear wiper should read? Possiblly just the switch that is bad (if all other wiring is good)?
Thanks

Time to change the Lgm with a used one. You are where I was when I swapped mine out. Bad LGM on mine took out all rear hatch functions except the license plate lights
 

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