Almost at my wit's end with the LGM. Please help :(

[esbob]

Just bought the TrailBlazer about a month ago.

Long story short, about a week after I bought it, the keyless stopped working, along with everything in the tailgate. I researched this forum and found that wires can be bad, and the module can be bad too. I pulled the LGM fuse (the 30amp one) and put it back in, voila everything worked again! For about a day. So then I tore the tailgate apart and checked all wires, everything looks perfect. I unplug and plug the LGM back in and everything works again! On the 3rd day I decided to put the tailgate back together. Worked until the next night - WTF

The LGM pins were bent so they weren't making good connection, and one plastic tab was broken on the LGM itself telling me someone was already messing with it. Like I said all the wires look perfect, and I did continuity test on them with no problems. Do the LGM themselves ever go to crap? I bought a new one and tried it but the rear wiper and RAP didn't work.

This is so f-ing frustrating, someone please help me and tell me what to do.

Thanks!

 

[The_Roadie]

When you said you checked continuity, where did you put the meter? One end at the wiring (using the pin through the insulation trick) at the vehicle side of the hinge area, so you're checking the most common failure point - where they flex? Bad communication is a huge source of problems - very frustrating to locate the problem if it isn't at the hinge area, but it could be all the way forward to the under-rear-seat splice pack. Flaky power could also be a root cause. Assume you checked the other power pins?

The new LGM might be the cure, but evil GM made it so you have to get it configured by a dealer with the Tech II tool like a BCM, if I remember correctly. Better troubleshooting would be to find a buddy and swap with them for a few minutes.

When you say "everything" are you including the license plate lights? Might point to a bad ground. Rear wiper dead?

 

[esbob]

Thanks for the quick reply.

First time I took the gate apart, I unplugged the harness and checked continuity from the harness end going into the tailgate and at the LGM. I wiggled harnesses and wires and nothing, until I got to the one harness on the LGM. If I wiggled IT, the liftgate would make that lock / unlock noise. Basically from what I can tell, it makes this noise when the LGM is initially plugged in. So I looked and the pins on the LGM looked like they were bent (from someone not me) to make less of a contact. I bent them to be making more contact. I have 12 volts at the orange wires, and ground on the black. Checked this while thoroughly moving around the wire harness going from tailgate to truck, and wiring in tailgate. Readings stayed the same.

Everything worked good for a day, basically til it got colder out. I opened the gate, unplugged LGM and plugged it back in - problem solved. For a day or so again. Right now nothing works, no wiper / keyless / can't open the rear, BUT the license plate lights do work. If I had a friend with another module it wouldn't help, unless I could leave it in for a couple days... seems it needs a couple days before it shits itself.

So I have a brand new LGM, superceded part number. With this one, the liftgate at least locks / unlocks and I can open the glass, but RAP, rear wiper don't work, didn't try to program keyfobs to it. So I'm still using the old one. If I call the dealer will they know what the deal is with programming the new LGM?

Thanks for your time and expertise Mr. Roadie!

 

[CaptainXL]

You can take the lift gate module apart and inspect the solder at the board. Which would present itself as an intermittent problem. A typical scenario would be that the previous owner bent the pins so it forces the solder connections against the board hoping it would work. Are you good with electronics?

 

[esbob]

Yeah I'm pretty familiar with electronics, I should pop the LGM open and see if the solder points are messed up. I think the pins were bent to make better contact on the harness but never thought of what thatd do to the inside of the LGM.

 

[dmtaurus]

I just saw you post so I hope it's not too late. There is an advertiser, on a radio show, that I think is called ModuleMaster.com. They rebuild modules and gage clusters and return them to you. The prices look to be really reasonable. The show is on WJR in Detroit on Saturdays. I hear it because the signal reaches me in Ohio. But you can also hear it online at WJR.com. It's called "The Car Show" and the guys that host it are really top-notch technicians.

I too had a lift gate module go bad. My wife had just gotten a bunch of groceries, lots of frozen items, and it was a hot, Saturday, summer day. At the store she put stuff in the cargo area and when she went to get it out at home none of the doors or liftgates would open. I unloaded the groceries and took it to the Chevy dealer. He said the module went bad and that he could override it to at least unlock everything. He didn't have one on hand, and would order one, all under warranty. He said these are a problem part on Trailblazers. I am glad that the part and labor was covered because he said it was about a $250 bill. I'll bet the PC boards have solder joints that go "open" when outside temps go up. I hope this helps.

 

[CaptainXL]

The 2005-2006 timeframe was when manufacturers needed to start worrying about becoming RoHS compliant. Its just more than likely a bad solder job. It probably had a bit to do with the ddm as well.

 

[dmtaurus]

The 2005-2006 timeframe was when manufacturers needed to start worrying about becoming RoHS compliant. Its just more than likely a bad solder job. It probably had a bit to do with the ddm as well.

You are right. The EPA and all the regulators have tried to get the lead out and forced the use of "green" fluxes which has led to poor wetting of solder joints and failing electronics. We have special exemption where I work to use 63/37 because our products go on commercial and military aircraft. Such stupid regulations that end up costing us all more money, and don't help the environment at all by causing the dumps to fill with more inferior PC boards.

 

[esbob]

Very interesting info, guys. Thanks. I won't be able to tear into it for the next couple days, but I'll pull it apart and let you know what I find.

 

[C-ya]

Quick question - what is "RAP"?

ETA: Saw the acronym was indeed underlined and essplained.

 

[Wooluf1952]

Quick question - what is "RAP"?

ETA: Saw the acronym was indeed underlined and essplained.

Hover your curser over the underlined letters.

 

[NJTB]

Retained Accessory Power

 

[esbob]

Ok, so I put the new LGM back in today. Nothing with it works, though it does lock the rear window when the hatch is open, then unlock it when the hatch is closed so that part is good. Going to the dealer tomorrow to have them program the new module.

I took the old one out and slid the board out of it, can't see anything wrong with it but maybe that doesn't mean anything.

 

[CaptainXL]

Can you get a real good closeup of the areas outlined in yellow? There doesn't appear to be much solder at these points.

View attachment 24209

 

[esbob]

Yeah I can do that. I put the new LGM back in last night, going to the dealership this morning to get it programmed. Hopefully this fixes my issues.

 

[CaptainXL]

Yeah I can do that. I put the new LGM back in last night, going to the dealership this morning to get it programmed. Hopefully this fixes my issues.

Ok, then I guess we are done here. No sense in taking the pictures.

On second thought please take the pictures. If there is a solder problem there then it might help out people in the future. It would be nice if resoldering fixes the issue. Will save you some money for programming.

 

[esbob]

Went to leave for the dealership this morning, and my battery was dead.

So jump started it, finally got it started up and nothing in the interior worked. Drove the dealership and the big fuse was blown, replaced that and fixed all the interior stuff. They programmed the new LGM and now everything is working ok. I will let you all know if it works in three days, that'll be the real test.

 

[Wooluf1952]

Can you get a real good closeup of the areas outlined in yellow? There doesn't appear to be much solder at these points.

View attachment 10904

The solder points on the back of the board look good. (Post #13)

 

[CaptainXL]

Went to leave for the dealership this morning, and my battery was dead.

So jump started it, finally got it started up and nothing in the interior worked. Drove the dealership and the big fuse was blown, replaced that and fixed all the interior stuff. They programmed the new LGM and now everything is working ok. I will let you all know if it works in three days, that'll be the real test.

OK, but we really could use those closeups. Thanks.

 

[CaptainXL]

The solder points on the back of the board look good. (Post #13)

Yes but those points on the back are electrically isolated and connect to nothing. The top portion of the PCB actually makes connections to the IC's via the traces.

 

[C-ya]

Yes but those points on the back are electrically isolated and connect to nothing. The top portion of the PCB actually makes connections to the IC's via the traces.

If they are soldered through like that and are isolated on the top (or bottom) of the board, then the connection is through the via - the hole in the PCB itself. It will be metallic and the solder will connect the top, bottom and the pin all at once.

 

[CaptainXL]

If they are soldered through like that and are isolated on the top (or bottom) of the board, then the connection is through the via - the hole in the PCB itself. It will be metallic and the solder will connect the top, bottom and the pin all at once.

I don't think the bottom of the pin is soldered to anything. It's just a ball of solder holding the pin down so it won't pull through the board. It sounds like you are talking about some type of sleave throught the board that goes to the top. I guess anything is possible.

 

[C-ya]

I saw it all the time when I worked at Whirlpool in the Electronic Development Lab, where we were constantly reworking boards for some test or another. Maybe that's why I thought it was more common. I guess it depends on who designs the board.

If you look at the pic of the bottom of the board on the holes with no pins, you can see a ring of metal. That's what leads me to believe the vias are plated.

 

[CaptainXL]

If you look at the pic of the bottom of the board on the holes with no pins, you can see a ring of metal. That's what leads me to believe the vias are plated.

i saw that too. Its possible. Would have to check it out with an ohmeter from top to bottom. I usually only saw stuff soldered like that in the aerospace industry but then again these boards might have similar requirement for vibration/heat resistant, etc.

The cold soak symptoms the OP was describing fit more with a cold solder joint so that's why I took off down this path. It would be the easiest thing to diagnose.

 

[dmtaurus]

i saw that too. Its possible. Would have to check it out with an ohmeter from top to bottom. I usually only saw stuff soldered like that in the aerospace industry but then again these boards might have similar requirement for vibration/heat resistant, etc.

The cold soak symptoms the OP was describing fit more with a cold solder joint so that's why I took off down this path. It would be the easiest thing to diagnose.

I work in the aerospace industry and many of our pc boards are multi-layered boards where the traces are sandwiched between the sides of the board. More conduction paths can be created within a smaller area. The only trade-off is that the board gets thicker. It is hard to figure what path conducts to what hole without the actual board trace drawing. Boards of this type have conducting, plated-thru holes, so that a conduction path for the traces can be created between the layers. I don't know for sure if the auto industry uses this type of board construction.

 

[The_Roadie]

I work in the aerospace industry and many of our pc boards are multi-layered boards ...

Very cool. My most complex PCB is 0.093" thick and 22 layers. We use FR4 at 0.004" thickness to build this one - same thickness as a typical sheet of 20 pound copy paper.

My experience with automotive electronics outside the expensive and performance-demanding PCM and Airbag controller, is that if they can save a dime by making a SINGLE-layer PCB, they will. Most things like random intelligent modules are two-layer. I've seen many single-layer boards that almost needed to be two layer, but the designer found a way to use a few (2-5) wire jumpers on the component side of the board to avoid needing that second layer. The economics are all strange (to me) when you're building things in the millions. Appliances, cheap power supplies, electronic ballasts for fluorescent lights - all done with low-end single-layer PCBs. A huge PCB run for my company is 300. (My experience comes from touring a few Delco/Delphi plants around the world, and Motorola in Texas, who made 1990-vintage Ford engine computers, all customers in the past. I helped design the tester for the Cadillac night vision thermal image sensor in the early 2000s for Delphi and got two trips to Singapore out of that project.)

 

[esbob]

Guys, the new LGM fixed my issues. It has been ten days, using the liftgate, cold and cool temperatures with no issues. That is great. However a new issue has presented itself today, which I will be posting about in the drivetrain forum. Thanks everyone for your help, I LOVE this website!

 

[CaptainXL]

Guys, the new LGM fixed my issues. It has been ten days, using the liftgate, cold and cool temperatures with no issues. That is great. However a new issue has presented itself today, which I will be posting about in the drivetrain forum. Thanks everyone for your help, I LOVE this website!

Good news. Please post the closeups asked for earlier. We would like to see if there is a solder problem on the PCB. This will help future members. Thanks.