Rear defrost

[dla442]

It don't work! Got 14.5 volts when car running and just over 12 when off at the clips on the window when they are removed. When one clip is attatched to window and one is off still 12 thru 14.5 volts. When one clip on window voltage is present on the grid when tested 12 thru 14.5 volts present. Several locations on grid tested with just one clip attached and all good. When I put the second clip on to complete the circuit and test the voltage, the voltage goes nil, even on the connecter, the place that connects to the grid and everywhere. It seems when both grid connections are on the window the volts go away. There is continuity from left to right and up and down each line in the grid.

Could it be there is such a small break that the whole window grid fails when 12v applied to the grid? Very odd...no clue what to do. No visual breaks and each line from end to end shows continuity. Wonder if where the connection to the grid is has lost connection beind the soldered joint?

Any advise would be great.

 

[IllogicTC]

I believe there was a TSB about this! But it was about how to properly reconnect the solder joint, not necessarily any known issue with the joint itself.

[media]https://www.youtube.com/watch?v=R0ZKoK_x6XM[/media]

 

[BlazingTrails]

You most likely have a broken wire between the body and hatch where the wires bend. When there is no load you are getting voltage but under load it drops out because the wires are close enough to get a reading but not enough to carry the amps.

 

[dla442]

The grid as far as I can test has no breaks...volts go away when the second wire to the grid is attached. I chased positive and negative under the seats and have continuity and power for the positive side. All wires in the hinge has been already replaced due to the breaking problem.

 

[BrownHP800]

Had a similar situation on my son's Cobalt. I had voltage at the clips when they were not connected to the grid but would show 0 when connected. I ran a jumper wire from 12v directly to the 12v side of the grid and it defrosted. So I got to digging and in the Cobalt there was a connector in the back that had melted. I guess it made enough contact to give voltage as long as it had no load. I just spliced in a new wire and it was good to go again.

I would check for a cut wire going to the grid.

 

[dla442]

Spot on. Found the issue and the connector had melted, bypassed with a jumper....

 

[BlazingTrails]

Nice!

 

[AtlWrk]

Wish I would've saw this last night before spending two hours chasing down these exact same symptoms:

+12V when one connector is disconnected. Nothing when both sides are connected. Even connecting a diagnostic light from the +12V (driver side connector, purple wire) side to a known good ground wouldn't light. How can that be?

Finally clicked: voltage but no current = high resistance. Pulled the panels to get to the LGM and found this beauty: The terminal got hot enough to reflow the solder on the LGM circuit board. Again, GM? why can't you just properly size your electrical components?

 

[IllogicTC]

Interesting. I'm having an issue where only the two lines running right next to the connectors actually work. I do have a couple of chipped spots, but they are in the middle of a couple other grid lines and shouldn't affect the whole grid. Guess I'll have a look at that plug.

 

[AtlWrk]

For those who find this thread later:

The replacement connector (harness side) is part number 12052856 ($0.94)
The green TPA (may or may not be needed) is 15324456 ($0.36)
The exact terminals called out were not in stock but I found both 15324456 or 12162597 were close enough (get a few just in case).

All are available on Mouser.com.

I cut the purple wire (the one that burned) and crimped on a new terminal. I then removed the green TPA and the other wires/terminals from the old connector and put them in the new one (mind the order!).

Fortunately, as bad as my LGM looked, I was able to clean up the terminals enough where I was comfortable re-using it. YMMV. This is probably the easiest module on the vehicle to disassemble.

Good as new-ish.

 

[Bow_Tied]

Couple of newb questions:

LGM = lift gate module?

If so, is the module in the lift gate? If not where is the pictured connector found?

TIA

 

[Mounce]

Yes, lift gate module.
Yes, actually inside the lift gate.
I'm unsure of where that connector is, at first I thought it was the one on the glass but after a second look that's not it.

 

[IllogicTC]

Yes, lift gate module.
Yes, actually inside the lift gate.
I'm unsure of where that connector is, at first I thought it was the one on the glass but after a second look that's not it.

I'm fairly sure that connector is one that connects to the LGM. Haven't had the liftgate apart myself, but it's very possible for a module to have more than one connector to it, and previous posts hint that that connector is on the LGM itself.

 

[AtlWrk]

Yes the LGM has three connectors: one for switches/locks, one for the rear wiper motor and one for power/defrost. It will be obvious which is which when you get in there.

The power connector has two heavy gauge wires for the defrost and two smaller wires for powering the module itself.

After unbolting the LGM from the liftgate I opened it up (two tabs on the case) and carefully slid the circuit board out to inspect. The solder on the terminal had obviously reflowed (at least 350F or so). Fortunately, the circuit traces had not delaminated and after cleaning the melted plastic of the terminal I touched up the solder joint and put it all back together. I'm still a bit hesitant about using the defrost which is frustrating, but it beats shelling out for a new LGM.