08 Avant Rear Window Issue

[Alex D]

Hello,

I have an 08 A6 Avant with about 150,000 miles on it. It's been a great car but we are now getting to the stage where all the little age-related gremlins start popping up.

The latest of these is that the left rear window stopped working. I can hear the relays going when the switches are pulled, but nothing happens.

As a first try, I purchased a used motor and swapped out the existing unit. Boom, the window worked like a champ again. Then, a few hours later, nothing. Dead as a doornail again.

I pulled the panel again, unplugged the replacement motor and tried plugging it in again. Lo and behold, the motor was spinning just fine. Hmm. Just for a test, I tried plugging in the original motor again and sure enough, it worked just fine too.

I buttoned it up again, tested all the switches, reset the one touch and all was well. About an hour and a half later (without be driven) I tested it again and the left rear window is dead yet again.

I'm at a bit of a loss. It doesn't seem like the normal issues (bad regulator, wonky guides, bad switch or bad wiring in the hinge area) are the culprit since it works fine after being unplugged for a minute.

Any chance it could be the control box that the motor plugs into in the door?

I would greatly appreciate any tips or hints as it's getting warm here and my son hates that he can't roll down his window!

Cheers!
Alex

[VAG-Abound]

My initial guess would be that the high current supply or earth has an intermittent connection that "settles" open. Do you have a multimeter to test what is getting to the 2.5mm wires that supply door control module and then motor when it is working and not working?

[Alex D]

I do have a multimeter. I'll give that a try. Just to make sure I understand, you are saying to pull the plug that goes into the control module now that it isn't working, and also the motor, then reconnect, confirm the window is working again, and then pull and test to see what has changed?

Thanks!
Alex

[VAG-Abound]

Not quite. Test for voltages and resistance to earth when it is working so you know what is good, then again when it isn't working but disturbing as little as possible. A sewing pin through the wire that you can use to sense voltage may be helpful. Put a wrap of tape over it after removing. If you find something is losing its connection jiggle it see if it comes back. If so find break in wire.

[Alex D]

Got it, thank you! I will try to do some testing this weekend.

Thanks!

[Alex D]

Ok, so I didn't not get a chance to do any testing this weekend. A few too many projects around the house. However, when I went for a drive, I noticed something. If I push the switch to roll down the window, there is nothing, no sound no click of the relay. However, if I pull the switch up, you can definitely hear the relay (or something) making a slight clunk. It's the same noise as all the other windows make.

Wouldn't that indicate that power is getting back there inasmuch as it tries to roll the window up?

Again, please pardon my ignorance, auto wiring beyond basic stereo work is not my forte!

Thanks,

Alex

[VAG-Abound]

No problem, understanding what is there will help you track down the problem.

There are two supplies of power to the door / window. A low current one in narrow wires for the electronics, switches, etc to all talk to each other. There is then a high current supply in a thicker wire for the actual motor to spin. The low current bits signal the relay to close for the high current to flow. So entirely plausible for everything to click happily on the low current side but there be an interruption to the high current supply (or in the high current drain to ground from the motor).

Can you do the all windows down / up trick from your remote unlocking key? If that will take it down / up it suggests a signalling problem in the cabin buttons rather than a motor supply one.

Also occurred to me to unplug in-door then driver-door switches from their loom to make sure they aren't damaged and sending a "window up" signal all the time. Unlikely, but easy to check and it'd be frustrating to find it out after hours playing with small wires in a confined place.

The thicker wires are blue / green and white / grey. One should be ground and the other 12V, either continuously or when the motor is trying to run (depending on how smart the actual motor unit is).

[Alex D]

Got it, thank you. That makes more sense.

The all up/down with the key doesn't work either.

Sounds like it is definitely time to get the multimeter out.

Thanks again,
Alex