Rear Defroster Not Working - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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  #1  
Old 10-07-2011, 09:06 AM
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joefireman289 joefireman289 is offline
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Rear Defroster Not Working

So here is my issue. I searched on this and couldn't find anything that has the same symptoms so here it goes. 2006 Envoy SLT, 85K miles, no codes. The issue is my rear defroster is not working. I have heated mirrors and they are working. The treads that I have read about this, most of the guys also have an issue with the rear wiper not working as well as the key fob not locking/unlocking the lift gate. This is not the issue, my rear wiper works fine (although it sucks at cleaning the glass, I need to upgrade to the 07+) and the lift gate locks and unlocks with the key fob. I'm not sure if the LGM (from what I've been able to find) is my problem. Last night I checked the wires inside the boot on the top of the list gate and they all seem to be intact, no tears or broken wires. I did not check the voltage of the wires as I can't seem to find my fluke meter. I also checked to make sure that both connections on the glass were clean and connected correctly and looked for obvious breaks in the coating on the glass. My question is, am I missing something obvious or am I searching for this with the wrong terminology? Any help would be much appreciated on this and thank you in advance.
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  #2  
Old 10-07-2011, 09:28 AM
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Checking the voltage and ground at the connectors for the grid is the definitive test. If it's not the 30A rear fuse #3, it's the wiring to the grid. A $1.99 Harbor Freight backup meter might be a good purchase.
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Old 10-07-2011, 09:55 AM
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Originally Posted by the roadie View Post
Checking the voltage and ground at the connectors for the grid is the definitive test. If it's not the 30A rear fuse #3, it's the wiring to the grid. A $1.99 Harbor Freight backup meter might be a good purchase.
Roadie (Bill) who would have guessed that you would be the first to respond and help me out with this. I will be stopping at Harbor Freight tonight to pick up a backup meter and will check the voltage. As you know he who has the most tools/toy wins, and I could always use more tools. The fuse didn't even cross my mind because I thought the mirror defrost and the rear window defrost were on the same circuit/fuse. I'm going to go out at lunch and check fuse #3 under the back seat and see if that's the problem. If it is then all is good I have some spare fuses in the glove box (A tip I picked up from one of your right ups on all the stuff you carry when off-roading) Thanks again for pointing me in a direction with this roadie.
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Old 10-07-2011, 10:28 AM
SparkyJJO SparkyJJO is offline
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Mine doesn't work except for one line because the rest are all scratched off the glass. And replacement glass is expensive

Hope that's not your issue.
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Old 10-07-2011, 10:38 AM
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Originally Posted by joefireman289 View Post
:...who would have guessed that you would be the first to respond ...
You're the last lucky duck for five days because I'm leaving in a hour for my yearly expedition to the Sierra Nevadas and Death Valley.

But of course I'm not the only one with access to the shop manual.
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Old 10-07-2011, 11:58 AM
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You're the last lucky duck for five days because I'm leaving in a hour for my yearly expedition to the Sierra Nevadas and Death Valley.

But of course I'm not the only one with access to the shop manual.
Enjoy the Nevadas and Death Valley. I have access to an aftermarket manual but it's more of just a how to fix, not a how to diagnose book. Not really a good $30 investment.

I went out at lunch and pulled the #3 fuse and it's good. I also checked #19 a 10A fuse that is labled with LGM and it is good also. So I guess its off to Harbor Freight to get a new meter and start checking voltages. Thanx again for the direction.
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Old 10-15-2011, 09:40 AM
fishguy1123 fishguy1123 is offline
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Any updates on this? I think I might have the same problem. Fuse is good also... Thanks
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  #8  
Old 10-15-2011, 01:20 PM
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Another way to check for breaks in the heater lines on the glass is to use a flashlight shining outward from the inside.....you can see where the coating has been scratched off or broken, pretty easily.

Repair kits are available at most auto parts stores, or here:

www.frostfighter.com
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  #9  
Old 10-17-2011, 09:03 AM
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Any updates on this? I think I might have the same problem. Fuse is good also... Thanks
No resolution to this problem yet. I check the voltage on the electrical lines inside the boot at the top of the lift gate and they check good as did the ground, no corrosion and it was tight. I'm going to try the flashlight trick and see if there is maybe a break in the lines on the glass somewhere. If there is a break I would assume that it has to be close to where the connection is to the glass, as none of the lines are working. Petevw thanks for the tip and the link, much appreciated.
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Old 10-27-2011, 08:03 AM
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After further inspection of the grid on the glass I found no breaks in the lines or scratches that would cause an interruption. I re-checked the voltage on all the connectors inside the boot and all tested around 13 volts. I checked the voltage where the wires plug into the glass grid on each side and the results were not good. The driver side tested fine but the passenger side had only about 1.3 volts. I'm going to take the trim off this weekend and do some more investigation of this problem. I'm going on the assumption that there is a break in the line between the LGM plug inside the boot and the connection at the glass on the passenger side. Am I going in the right direction with this or am I just wasting my time? I cannot find a wiring diagram of the lift gate to see if there is a fusible link or possible pinch point under the trim at the top of the glass. I'm also wondering if there is a way to test the LGM that is in the fuse block under the rear seat, and if so would I be testing it for just resistance or for voltage drop? Thank you in advance for reading and helping.
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