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My rear defroster is not working. Relay works, fuse appears to be ok. Getting 5 volts at connector on rear window on passenger side when defrost turned on. Have 12V coming into relay under hood. Any idea why I might be getting 5V at window? I would assume it should be 12V. Defrost really doesn't work right now which is a pain as it is -25 C right now. Can't find wiring diagrams in Haynes or online.

Thanks for any help.

 
Rep Power: 519

Coupe or sedan? They are a little different.

Are you checking power at the defogger grid, or are you checking at the antenna grid?
Antenna is at the top, defogger connector is midway down the side of the glass.

Because of the antenna grid on the glass, it may not be a simple power and ground. The defog grid power may run through an antenna module and/or a 'coil' (looks like it may contain resistors and a noise filter).

 
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It is a 4 door sedan.

Voltage was measured on tab halfway up window. Took the connector off and cycled power with the defrost switch and measured about 5 volts. I believe the antenna connector is under the trim panel which was not removed.

I am assuming it should be 12v at the connector. Can't find proper wiring diagram to see how it is fed with power or where the harness runs. I measured 12volts at the relay under the hood (with relay removed). Relay appears to work.

 
Rep Power: 519

Open trunk lid, look under speaker shelf between the seatback lock cylinder and the right speaker, there should be an odd shaped box, black cover with slits in it, with 2 connectors in it.

The single wire connector is the B+ power, comes from the relay. Should have full 12v on it. (black wire) EDIT: should have full 12v on it when the defogger is turned on

The box is grounded in the mounting screw.
The other connector has 2 wires (both black), each wire goes to one side of the defog grid. one should be power, the other should be ground.

 
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It has 4V at connector and at the box. Any suggestions?

 
Rep Power: 519

Single wire connector at that box only has 4v ?

I'd probably jumper the socket for the relay contacts and triple check there is actually 12v while loaded (not chasing a ghost from a bad fuse or something before the relay), then follow the harness from the relay box to the trunk.

There should be 2 harness connectors in this circuit.....One harness connector (single wire) is on what looks like the right side of the center console/lower dash-floor support after all the console forward trim is removed (sorry, don't have a real car to look at here), and the other harness connector (14 cavities, the largest one is the defogger wire) is found between cabin and trunk covered by the rear seatback right side bolster,,,,,about equal height with the rear door striker loop.

 
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Thanks for you help. Good suggestions, I'll check that out.

 
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Seems to be a problem in the connector beside the rear seat. Getting 12V on one side and a few volts on the other side. Just need to figure out how to separate the connector! I thought I was getting it apart but it seemed the backshell was just coming apart so I didn't push any further. Can't figure out how to release the two halves.....

 
Rep Power: 519

I sure can't see what you are dealing with......One connector half will have a tab in the center that must be pressed in to release the lock, then the connector halves can be pulled apart. Sometimes they are not easy to pull apart. If you can't get the lock tab to push down, try squeezing the connector halves together first and retry.

Similar (googled pics)





If you are trying to get both halves to release off of a mounting tab, there should be yet another lock tab in the area of the mounting tab that needs either lifted or pressed, depending on the design. If there is corrosion present on the metal tab, it may take some wiggling and maybe force to get it free from the tab.

 
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Thanks. Part of the problem is the space is tight. Hard to get hands and work on it. I'll try when I have a bit more light to see it better.

 
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The problem was in the connector by the rear right seat. Took off the seat trim to expose connector (can also be seen from hole inside trunk). Not real easy to get at but was able to get it apart.

The pin carrying the 12V for the defrost was no longer seated well due to the fact that the connector shell had partially melted allowing the pin to move. I think the melted connector was also the reason why I couldn't get it apart earlier.

We are going to installer a jumper around the connector for the defrost wire as the pin is not repairable. The other pins still look ok.

I think that should resolve the problem. Thanks for all your help eZone!

 
Rep Power: 519

Melted around that pin probably means that pair of contacts had a lousy connection or high resistance and subsequent heat buildup (resistance + load = heat).

I'd jumper around the bad spot too, should be good after that.
Good luck!

 
Rep Power: 309

^^^ With no voltage to the grid.... this is what you should focus on next.

Edit: Wow too many post... replied to wrong one.