BCM, LCM, or something else ?

[truck2trail]

I think ALL the items below just quit one day recently: i.e. it looks like one overall unit (the LCM ?) suddenly quit one day, but I didn't notice some of the items failing until actually testing them:

1) Key fob, despite new battery - just quit working one day - first thing I noticed. Replaced battery, still no go.
2) Rear wiper or wash, no matter how I use the switch. Don't use these much in the summer, but upon trying, they don't work !!
3) The tailgate doesn't lock when I lock the side doors. I can still open the back window with the push button when side doors are locked. Only just noticed this.
4) Radio goes off as soon as I switch engine off - used to stay on until I opened the door, or for a few minutes if I just sat in the car with the doors locked. (I frequent scary places !!!). Didn't notice this until testing.
5) The interior lights stay on in one of the push button positions even after I've closed the doors during the day time. I have to keep the push button on the LHS in one position only. Noticed this about the same day as the key fob didn't work.

The following items are still working:

a) Side door locks, but only from the switches inside on both the driver's and passenger's side arm rests.
b) All the power windows
c) Daytime running lights (car was built in the USA, but to Canadian requirements)
d) Front windshield wipers, including intermittent positions. Aslo wash.
e) Heating and A/C controls
f) Licence light

Defroster - can't tell in this weather.

I've checked fuses 3,6,9 in rear and 7 in front - all OK. I've checked the wiring at the hinge - the rubber boot looks a bit worn, but not severely. The wire going to the inside roof light at the rear looks OK.

Unfortunately, I can't test any voltages as my meter is 100 miles away on the sailing boat !!

Any verdict, given the above ? Suggestions for further diagnosis ? Thanks.

I've just gone and checked them - took the rubber boot off at both ends, wires are perfectly new and unblemished !

 

[The_Roadie]

I think all LGM (Lift Gate Module) functions are suppressed if it thinks the latch is ajar. I'd start by taking the interior trim panel off and poking about and lubricating the latch area to free up the switch that detects the state of the liftgate.

 

[truck2trail]

I think all LGM (Lift Gate Module) functions are suppressed if it thinks the latch is ajar. I'd start by taking the interior trim panel off and poking about and lubricating the latch area to free up the switch that detects the state of the liftgate.

I've read many of the postings about removing the interior trim panels (including removing the top panel first), but I've never seen any mention of how to remove the black hand insert/pocket in the bottom of the trim panel that's in my 2007 TB. There's no screw inside or near to the insert/pocket and I'm afraid to pull hard on the panel in case I break it. I don't think I can remove the panel before removing this insert/pocket.

It seems the function of insert/pocket is put your hand in it to assist in pulling down the tailgate. Similar to the strap that was in earlier models. Any suggestions as to how to go about removing it would be helpful ! Thank you.

 

[McGMT]

I've read many of the postings about removing the interior trim panels (including removing the top panel first), but I've never seen any mention of how to remove the black hand insert/pocket in the bottom of the trim panel that's in my 2007 TB. There's no screw inside or near to the insert/pocket and I'm afraid to pull hard on the panel in case I break it. I don't think I can remove the panel before removing this insert/pocket.

It seems the function of insert/pocket is put your hand in it to assist in pulling down the tailgate. Similar to the strap that was in earlier models. Any suggestions as to how to go about removing it would be helpful ! Thank you.

IMHO, if it was me I would try removing the trim panel starting from the top to see if it needs to be removed before trying. I am sure someone else has taken theirs off but since they haven't responded yet I figured I would give you my .

If it does need to be removed then it would have to be clips like most the other "junk" in our interiors. Just try using two wide blades, one on each end to reduce strain on the plastic so you avoid the horrifying "SNAP" sound haha....

Good luck....

 

[truck2trail]

IMHO, if it was me I would.......

Yes, I was mistaken, it is not necessary to remove the hand insert ! I hadn't tried hard to remove the bottom trim panel ! Good job as well, for when I did get the bottom trim off, that hand insert is firmly stuck into the metal frame ! I only loosened the bottom two clips of the upper trim panel, as that was sufficient to get the bottom panel off.

However, back to my main problem. The metal parts of the tailgate switch/lock are in good shape, i.e. the left and righthand rods work very well, as does the rod to the window push button.

With the help of my next door neighbour's meter I was able to ascertain the following:

1) There is 12v on the Orange cable where it goes into the LCM/LGM. I'm assuming the LCM/LGM is the black module (about 4" x 6") on the lower RHS (looking from inside the vehicle) of the tailgate.

2) There is 12v on the orange (O) cable that goes into the rear wiper motor, measured using the black cable in the same plug, and using the body of the tailgate as ground.

3) The black (B) cable in #2 above is a good earth, measured using the ohm-meter.

4) Nothing from the grey (G) cable that also goes into the wiper motor connector, i.e. no volts between G>O, or G>B

5) Fuse 7, feeding the Rear Window Wash is OK, as are the Relay switch pins.

6) Did I say previously that the cables in the boot near the hinge between the body and the tailgate are very good ?

7) I did notice that when I replaced the connector into the LCM, there was a "buzz" which sounded like a lock working, but I didn't see anything move ! I repeated this a number of times and found I had to wait 30 seconds in between tests.

I'm prepared to purchase either BCN or a LCM --- BUT WHICH ?? Based on the circuit diagrams in the Chilton Service Manual, (Radio problem, courtesy lights problem) I think now I'm leaning towards the BCN being the culprit, but don't understand how some of the other functions it controls are OK.

Are there any definite checks I can make to determine which it might be ? Thanks for any responses. I'm placing all my hope in THIS and only this board !

 

[The_Roadie]

Swapping with a local buddy is the best diagnosis. If you buy a used module (either one) from Ebay, the option list may not match yours and then it's an additional expense of a dealer visit. New unused ones are guaranteed to need a dealer configuration visit. Actually, I'm not absolutely certain if an LGM needs to be configured.

 

[jimmyjam]

I'm prepared to purchase either BCN or a LCM --- BUT WHICH ?? Based on the circuit diagrams in the Chilton Service Manual, (Radio problem, courtesy lights problem) I think now I'm leaning towards the BCN being the culprit, but don't understand how some of the other functions it controls are OK.

i vote the LGM is the problem. you are correct in thinking the bcm is controlling the lights/radio, however it could be that it is affected by bad information garnered from the LGM (telling the bcm that the liftgate is opened)

its times like these that it helps having a friend with access to a tech2 as it can diagnose all these modules. you can pony up for a dealership diagnostic, or try crossing your fingers and swapping parts. not ideal, but in the era of databus-linked modules, there isn't really a way to know what is at fault without the proper tools.

 

[truck2trail]

i vote the LGM is the problem.........its times like these that it helps having a friend with access to a tech2 as it can diagnose all these modules. ......

Yes, I wish !! Unfortunately, most of my friends just take their car the the stealership ! Wow, those tech2's are expensive. I looked for codes on my Scanguage II but it didn't show any. Any good if I dig deeper into the Scanguage ?

I just want to share with you an answer I've just received from "Just Answer" (I'm getting desperate !)

""The thick black to the LGM is the ground so please check that. If that is good then try taking the battery cables off the battery and touch the ends together for ten seconds and see what happens. This resets the modules.

See what this does and let me know."

OMG !! I don't think so !

You know, I think I'll take it to somewhere for a diagnostic check. Do I have to take it a Chevy dealer, or do "back street" garages have tech2's ??

 

[ScarabEpic22]

Sounds like exactly what my 02 did about 18 months ago, radio would shut off after removing the key like a door was open, liftgate didnt lock/unlock with the fob (or door switches for me), and the rear wiper stopped working. I pulled the rear trim and looked at all the wires too, one of mine was messed up I believe and I had to fix it. Still didnt fix the problem so I bought a new LGM off eBay for like $25 and then paid a stealer $125 to program it, ugh. Its worked great since then though!

 

[truck2trail]

........so I bought a new LGM off eBay for like $25 and then paid a stealer $125 to program it, ugh.

Maybe my best approach is to take it to a dealer, get the test done, drive away and go back later with a new LCM (or BCM), that I've purchased from Ebay or a wholesaler, and installed. They then can configure it if necessary.

Just as an aside - is there any merit in the answer from "just Answer" above ?

 

[MAY03LT]

3) The black (B) cable in #2 above is a good earth, measured using the ohm-meter.

That's not a good way to verify a good ground. There could be one strand of copper connected that would make it pass a continuity test. I got turned on to the "super test light", where you use a sealed beam (4-6A) headlamp and some extra long jumper leads to load down the suspected bad ground.

You know, I think I'll take it to somewhere for a diagnostic check. Do I have to take it a Chevy dealer, or do "back street" garages have tech2's ??

For a diagnostic, it doesn't have to be a tech 2. Other high end scan tools like the snap on modis or verus can read other modules like the bcm/lgm.

 

[truck2trail]

"Try taking the battery cables off the battery and touch the ends together for ten seconds and see what happens. This resets the modules."

What do you think ??

 

[jimmyjam]

just leave them unhooked for 15-30 minutes

 

[truck2trail]

just leave them unhooked for 15-30 minutes

Sounds a better idea !! Thanks. This clears the PCM and screws up the idling etc ? Any tips on how to handle THAT situation ?!! I don't want to dig a bigger hole than I can't get out of !

 

[jimmyjam]

Just pull the lgm fuse

But I don't think it's going to accomplish anything

 

[The_Roadie]

This clears the PCM and screws up the idling etc ?

Driving around normally in the city for a short time fixes that if the throttle body is clean. If a battery disconnect takes out an HVAC actuator, well, then, it was weak and needed to be taken out and shot. If it screws up the idling too badly, then you needed to clean your throttle body anyway. Almost no downside, since you could accidentally discharge your battery at any time, and better that things fail when you know about them and can fix them rather than on a trip or winter time or in a dodgy neighborhood when it's harder.

 

[truck2trail]

Just pull the lgm fuse

But I don't think it's going to accomplish anything

I think I may have done this already out of curiosity !! Is it the small two wired white plastic item, 0.5" by 2" (approx) in the middle of the tailgate, with black & grey wires ? Looks like two cylinders side by side ? Does it actually have fuses inside it ? I opened it at one end and didn't see any fuses.

Driving around normally in the city for a short time fixes that if the throttle body is clean. If a battery disconnect takes out an HVAC actuator, well, then, it was weak and needed to be taken out and shot. If it screws up the idling too badly, then you needed to clean your throttle body anyway. Almost no downside, since you could accidentally discharge your battery at any time, and better that things fail when you know about them and can fix them rather than on a trip or winter time or in a dodgy neighborhood when it's harder.

Good point. Thanks.

 

[truck2trail]

It was a broken thin wire (blue) in the boot after all !

I had booked the truck in for this morning in desperation, but last night I thought I'd take one last examination of the wires in the boot in the hinge area between the body and the tailgate. Previously, I'd looked at the wires, and all seemed OK. This time I pulled on each wire, and of course, it had to be the last one, that just kept coming until I saw the break ! I fixed the break and now everything works OK again.

So my apologies for raising a false alarm and wasting everyone's time ! If I'd done a better examination in the first place, I'd have saved myself a lot of worry, and a lot of needless typing from responders !!

 

[MAY03LT]

So my apologies for raising a false alarm and wasting everyone's time !

You didn't waste anyone's time, that's for sure.

Thanks for coming back and posting the fix!

 

[6716]

Just double checking everything.

So y'all know, I've been through all the threads here and on the OS that I could find.

Everything on the liftgate works EXCEPT the locking mechanism.

I open the liftgate a good 10 times a day for work, usually I lock the vehicle as a habit. About 3 months ago it started that I could open the liftgate even when the car was locked. The alarm would go off. Yesterday I started messing with it, moved the latch/lock bit with a screwdriver. Now it opens when the car is locked BUT the alarm DOESN'T go off.

Lic plate lights work; rear wiper, check; rear wiper fluid, check. Key fob works to lock everything but the liftgate. Radio stays on when the key comes out until I open the driver's door. Liftgate ajar dash light works.

Today removed the trim.

Removed locking mechanism, cleaned up with penetrating oil. Found the black plastic encasing the moving latch bit was chewed up, removed chewed up bits (with a sharp blade). Confirmed (relatively) smooth movement of locking bit. Reinstalled locking mechanism.

Looked for broken wires in the boot, didn't find any (but then, not having any other problems, so not surprised).

Mechanism makes noise when the connectors are removed/installed. Also makes noise when connector is removed/installed at LCM.

Sat in the back, closed the hatch, hit the locks, saw movement in the mechanism, but it just doesn't lock.

Don't have an electric meter, wouldn't know what to do with it if I did, anyway.

Anything else I can try before I spend the money on a new unit? I found a link through the OS Chevy TrailBlazer Keyless System - Car Forums - Edmunds (the good bit is at the end) that might be the answer, though I don't know that I understand it, anyway.

Thanks for your thoughts.

 

[Denali n DOO]

Just double checking everything.

So y'all know, I've been through all the threads here and on the OS that I could find.

Everything on the liftgate works EXCEPT the locking mechanism.

I open the liftgate a good 10 times a day for work, usually I lock the vehicle as a habit. About 3 months ago it started that I could open the liftgate even when the car was locked. The alarm would go off. Yesterday I started messing with it, moved the latch/lock bit with a screwdriver. Now it opens when the car is locked BUT the alarm DOESN'T go off.

Lic plate lights work; rear wiper, check; rear wiper fluid, check. Key fob works to lock everything but the liftgate. Radio stays on when the key comes out until I open the driver's door. Liftgate ajar dash light works.

Today removed the trim.

Removed locking mechanism, cleaned up with penetrating oil. Found the black plastic encasing the moving latch bit was chewed up, removed chewed up bits (with a sharp blade). Confirmed (relatively) smooth movement of locking bit. Reinstalled locking mechanism.

Looked for broken wires in the boot, didn't find any (but then, not having any other problems, so not surprised).

Mechanism makes noise when the connectors are removed/installed. Also makes noise when connector is removed/installed at LCM.

Sat in the back, closed the hatch, hit the locks, saw movement in the mechanism, but it just doesn't lock.

Don't have an electric meter, wouldn't know what to do with it if I did, anyway.

Anything else I can try before I spend the money on a new unit? I found a link through the OS Chevy TrailBlazer Keyless System - Car Forums - Edmunds (the good bit is at the end) that might be the answer, though I don't know that I understand it, anyway.

Thanks for your thoughts.

I'd go back and look at those wires in the boot again, I missed the broken one the first time I looked. My lock would move a little like yours does and after the wire was fixed it started to lock properly.

 

[6716]

I'd go back and look at those wires in the boot again, I missed the broken one the first time I looked. My lock would move a little like yours does and after the wire was fixed it started to lock properly.

Fair enough. I'll go back through it. Do you remember what color the broken wire was? I think I have one blue one and a bunch of orange ones.

Electrical makes my brain hurt.

 

[truck2trail]

Fair enough. I'll go back through it. Do you remember what color the broken wire was? I think I have one blue one and a bunch of orange ones.

Electrical makes my brain hurt.

I missed my broken wire at my first look.

DON'T just look at the wires, GENTLY tug each wire from both ends. When I did this, I found one of my very thin wires just came out of the boot altogether. I added another bit of wire with crimp connectors to each end and then everything worked fine.

 

[6716]

I missed my broken wire at my first look.

DON'T just look at the wires, GENTLY tug each wire from both ends. When I did this, I found one of my very thin wires just came out of the boot altogether. I added another bit of wire with crimp connectors to each end and then everything worked fine.

Man, I can NOT find it ... all the wires pull through each way, so none are broken. Maybe there's a short in there, where it looks like there's some electrical tape around the wires in the middle of the boot that I can't seem to get to.

Where can I read something on how to use a meter or something to figure this out? Anyone know?

Clearly, I need to get better at electrical.

 

[D0M0]

Yeah Im having the same issues too with the gate, but also my front seats stopped working as well. They wont heat up or move at all.

Was told this was a BCM issue. Im about to buy the part from Rockauto but was wondering if i should buy the LGM while im at it.

I checked the wires in the rubber boot area of the gate where it closes, nothing was frayed or broken. Maybe ill look again and tug. they was all taped together pretty tight.

I need for the seats to work so i can at least past inspection. MD is a pain in the.. you know the rest. lol

Could the LGM quit if the BCM isnt working as well?

 

[The_Roadie]

Who diagnosed it as a BCM issue? It might be, but there are ten other things it could be. The most obvious is the seat circuit breaker. CB8 in the rear fuse block.

If you buy a new BCM, you're going to have to go to the dealer and spend another $100 or so to have it configured.

The LGM and the BCM communicate on the main data bus, so they are certainly interrelated.

I'm very interested who gave you that simplistic diagnosis and if you paid for it.

 

[D0M0]

Who diagnosed it as a BCM issue? It might be, but there are ten other things it could be. The most obvious is the seat circuit breaker. CB8 in the rear fuse block.

If you buy a new BCM, you're going to have to go to the dealer and spend another $100 or so to have it configured.

The LGM and the BCM communicate on the main data bus, so they are certainly interrelated.

I'm very interested who gave you that simplistic diagnosis and if you paid for it.

Well, I bought the truck from a friend of mine. He had it looked at by a Chevy dealer about a month ago. So I didn't pay for it.

Is cb8 the fuse in the rear near the bcm? Ill check it and see if the fuse is ok. I'm open to any suggestions for now that will help me solve this issue,

 

[6716]

Well, I bought the truck from a friend of mine. He had it looked at by a Chevy dealer about a month ago. So I didn't pay for it.

Is cb8 the fuse in the rear near the bcm? Ill check it and see if the fuse is ok. I'm open to any suggestions for now that will help me solve this issue,

What I really want to do is convince my retired neighbor to swap out locking mechanisms with me from his Ranier ... but I don't see that happening.

Your seat and liftgate problems may not be connected. Locking mechanism swap-out is the next trick for me in troubleshooting the gate. It'll be a few weeks 'til I get to it, though.

 

[truck2trail]

Yeah Im having the same issues too with the gate, but also my front seats stopped working as well. They wont heat up or move at all.

Was told this was a BCM issue. Im about to buy the part from Rockauto but was wondering if i should buy the LGM while im at it.

I checked the wires in the rubber boot area of the gate where it closes, nothing was frayed or broken. Maybe ill look again and tug. they was all taped together pretty tight.

I need for the seats to work so i can at least past inspection. MD is a pain in the.. you know the rest. lol

Could the LGM quit if the BCM isnt working as well?

I don't have heated seats, I guess you must have a LT model ? However, based on my experience, before buying anything, I'd undo the taping around the wires and tug and see. Maybe the taping is holding together a broken wire. My wire had been pulled apart, i.e. it had got snapped, whereas some of the photos I've seen on this issue show the wires as bent up and frayed.

 

[D0M0]

I don't have heated seats, I guess you must have a LT model ? However, based on my experience, before buying anything, I'd undo the taping around the wires and tug and see. Maybe the taping is holding together a broken wire. My wire had been pulled apart, i.e. it had got snapped, whereas some of the photos I've seen on this issue show the wires as bent up and frayed.

I have the LTZ model. I'm going to check some fuse and wires first before I dive in buying new parts.

 

[D0M0]

Hey that circuit breaker was burnt up! I need to know what amperage it was to replace it

And apparently pep boys and AutoZone doesn't carry that particular breaker -___-

 

[D0M0]

So I replaced the circuit breaker and I replaced the LGM/DSM #6 fuse only to get everything to start smoking 0___0 apparently the #6 fuse blew as well help!!!

 

[truck2trail]

So I replaced the circuit breaker and I replaced the LGM/DSM #6 fuse only to get everything to start smoking 0___0 apparently the #6 fuse blew as well help!!!

It's usually a good idea to change one thing at a time. That way you get to know more about the problem. Start again doing this. Although you may have caused a new problem by now !

 

[D0M0]

It's usually a good idea to change one thing at a time. That way you get to know more about the problem. Start again doing this. Although you may have caused a new problem by now !

That's what I was doing. I was checking each fuse after the circuit breaker heated up and the seat still didn't move. found the #6 fuse had burnt out. Replaced it and it did it again and started smoking. Removed it immediately.
Hopefully I didn't cause any other damage. I'm going to take it to the dealer tomorrow and see what's up.

 

[6716]

I'd go back and look at those wires in the boot again, I missed the broken one the first time I looked. My lock would move a little like yours does and after the wire was fixed it started to lock properly.

Now that I've taken care of some other repairs, I'm back to this issue.

The main problem I have in checking all the wires inside that #$%&ing boot is that I can't move it around enough to get at the wires where there is some electrical tape covering them all ... somewhere in the middle of the boot.

Since the boot is causing the difficulty ...

Would it be really stupid to clip all of the wires, slide the boot off, inspect where I can't otherwise get to, make a slight repair if needed, slide the boot back on, and re-connect the wires?

I can't see much other way to get that boot out of the way.

 

[The_Roadie]

Would it be really stupid to clip all of the wires,

You'd be the first of hundreds of people to go that route. Take heart in the fact that everybody else has managed somehow to inspect the wires without destroying the reliability by cutting them. You might be able to use the old pin trick to check continuity without cutting into the wires. Just poke a needle or pin through the insulation into the center of the wire on each side of the hinge line, then use your meter to check continuity between the two pins. Best to disconnect the battery.

 

[Denali n DOO]

The boot is tight and hard to move along the wires, with the boot disconnected at both ends and plastic clips out, I recall pulling slack wire from the body side and pushing the boot up the wires squeezing the boot together towards the body. When I found my broken wire I dipped it in vasaline and easily passed it through the boot. Maybe a little vasaline on the wires before you try to slide the boot will help? Don't give up, it can be done. I wouldn't cut all the wires to remove boot.

 

[6716]

Thanks all for the tips.

I undid the 6-wire connector just at the body side of the boot, which gave me more working room. Eventually, this is what I found:

View attachment 22677

It's so small, I couldn't get the camera to focus correctly on it, so I don't know how well that is going to show up. It's the fattest of the three orange wires in that group of six total wires.

So .... I break out the electrical tape, tape it all up, inspect all the other wires in that area, don't find anything else, re-connect .......

and it still doesn't lock

actuator?

 

[D0M0]

Well I got the BCM programmed and all with no luck so I'm back at square one. *doh

The weird thing is that the circuit breaker is STILL overheating... What could be causing that?

 

[NJTB]

Well I got the BCM programmed and all with no luck so I'm back at square one. *doh

The weird thing is that the circuit breaker is STILL overheating... What could be causing that?

Sounds like you need a schematic.
Try this-disconnect the wires (via the connectors, don't cut them) to the liftgate and the seats, then try plugging in the relay. If it overheats, it could be a grounded wire. If it don't overheat, you probably have a component thats shorted/stuck on, or drawing too much current.
That's why you need the schematic.
Good hunting.