Rear Defroster Not Working

[joltman]

The past couple of weeks, we've had some mornings that have frosted up my windows. In the past, I would turn on the rear defroster and the mirrors and rear glass would defrost. However, now the rear window won't defrost. I thought this was an issue with a broken wire on the glass. However, I took a voltmeter to the 2 wires that connect to that "grid" (I disconnected them from the grid). I turned the key to the second position (just before START), and turned on the defroster. The light came on. I checked the voltmeter, and it was showing millivolts. Strange. So I checked each wire against a ground on the chassis. Either side didn't give me any volts (just millivolts).

I checked the fuse under the hood. It was a 30A and it was fine. I pulled the relay and ran a 9V battery across the coil side, and could hear the relay click. While 9V was applied, I tested resistance across the other set of terminals on the relay, and was getting no resistance.

Back under the hood, I took a volt meter to the same relay connection side in the fuse box. Pressing the defrost button and I saw 12V. I then connected the opposite set of terminals with my volt meter and saw 12V. Basically, this is telling me that the defroster button (switch) works, the relay works (as it clicks and tests 0 resistance), the terminals in the fuse box work as I can get 12V across the correct pairs.

In my head, this leaves only the wiring. This is where things get super fuzzy for me. Can someone help me out and confirm that I'm going about this the correct way?? Was my troubleshooting of the wires on the back window correct? I should be able to take off the wires from the back window and connect my voltmeter to each wire and I should see a voltage, correct? Any help would be REALLY appreciated. Thanks all!

Jim

 

[regguay]

Yukon rear defroster not working

Ok, I spent so many hours trying to find this problem and I found it with help of others on this forum. Rear defroster would work sometimes then stopped working. Was not getting power to the grid and fuse was good and switch was clicking on ok. traced wires back from dash and had power all the way back to the rear hatch then nothing. took the boot off from the rear tailgate where wires pass into the chassis up at the top and bingo. take apart the big connector that connects the wires at the hatch and badly burned wires, two of them, one defroster and one I suspect was wiper motor wire, these were badly burned and obviously lost their conductivity and no wonder when you look at the small connector used. Had to by-pass the connector by soldering wire extensions to the two damaged wires passed them through the connector and made two new connectors for the damaged wires. suspect wiper would have been next problem. Undersized connector obviously for the defroster and high current. All good now.

 

[joltman]

Ok, I spent so many hours trying to find this problem and I found it with help of others on this forum. Rear defroster would work sometimes then stopped working. Was not getting power to the grid and fuse was good and switch was clicking on ok. traced wires back from dash and had power all the way back to the rear hatch then nothing. took the boot off from the rear tailgate where wires pass into the chassis up at the top and bingo. take apart the big connector that connects the wires at the hatch and badly burned wires, two of them, one defroster and one I suspect was wiper motor wire, these were badly burned and obviously lost their conductivity and no wonder when you look at the small connector used. Had to by-pass the connector by soldering wire extensions to the two damaged wires passed them through the connector and made two new connectors for the damaged wires. suspect wiper would have been next problem. Undersized connector obviously for the defroster and high current. All good now.

I completely forgot I had not updated this thread. I'm really sorry!

You are 100% correct. The issue was the connection above the headliner just inside the rear hatch. I had the local Chevy dealership replace the entire rear hatch wiring harness. They said the issue was in that boot/harness that you described. Had I had more balls, I would have opened up the headliner and saw the same thing. Thanks for updating this thread!!