04 A4 sedan rear defrost doesn't work. Ideas?

[jesse500]

The rear window defroster in my USP stopped working. Did for a while, but nothing now. button in the HVAC lights up, but no defrost. VCDS says intermittent short to ground. Anyone had this issue before? I'm not too sure where to turn first. Relay, fuse? wiring that fails? No idea where the wiring for the rear defrost is hidden.

[diagnosticator]

There are several possible problems to check for. The rear window heating element on the glass might have a break somewhere. The wiring from the HVAC controller might have an open circuit, or a short to ground somewhere between the controller and the rear window. I don't recall a fuse in that circuit. If you know how to use a volt/ohm meter, you should be able to test the rear window element and the wiring as applicable. If the wiring is bad, or the heater element ground connection to the body is open circuit, run a new wire from the controller or to ground as needed.

[jesse500]

There are several possible problems to check for. The rear window heating element on the glass might have a break somewhere. The wiring from the HVAC controller might have an open circuit, or a short to ground somewhere between the controller and the rear window. I don't recall a fuse in that circuit. If you know how to use a volt/ohm meter, you should be able to test the rear window element and the wiring as applicable. If the wiring is bad, or the heater element ground connection to the body is open circuit, run a new wire from the controller or to ground as needed.

Is there a particular resistance reading I should get from window circuit? I realize if 0, then she broke, but I know its quite an intricate web of wires, still may have some resistance, but be broken.

[diagnosticator]

Is there a particular resistance reading I should get from window circuit? I realize if 0, then she broke, but I know its quite an intricate web of wires, still may have some resistance, but be broken.

I am not sure, the specificaton is in the Bentley, I will check that.

If the window heater is open circuit there will be infinitely high resistance, more than the meter can measure indicated by OL. or similar.

If the heater is shorted, or the power supply wiring is shorted to ground, the resistance measured from the hvac controller end will be lower than spec, and there could be continuity to chassis ground. That is, measurable resistance to chassis ground.
There should be no continuity aka an open circuit to chassis ground.

[A4orce84]

Hey Everyone,

Bumping this thread up since I have recently started experiencing a similar issue with my Rear Defroster not working! I did a quick scan of the car this morning with VCDS, and pulled the following related codes:

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 8E0-820-043.lbl
Part No: 8E0 820 043 AD
Component: A4 Klimaautomat 1324
Coding: 00000
Shop #: WSC 00672
VCID: 63C274CEF1CEF85994-515A

1 Fault Found:
00975 - Heated Rear Window (Z1)
31-10 - Open or Short to Ground - Intermittent

-------------------------------------------------------------------------------

I know it says intermittent in the code above, but I can confirm it has definitely not been working the past few times I've attempted using it. I wanted to ask if there are any fresh troubleshooting procedures, since this original post is a few years old. Any help would be greatly appreciated.

Thanks,
Asif

[Deerhurst]

Sound to me like either a broken wire or a wire with compromised insulation shorting to the body somewhere.

[Kevin C]

If I was going to guess it would be that the control unit was bad.

If you swap one to get clean looking buttons be aware of the different designs. This link give a lot of good info on fuses and swapping.


https://www.audizine.com/forum/showt...-in-early-B6-s