Passenger mirror tilt on reverse

[notorious]

It seems that the problem is potentiometer in the mirror assembly. Potentiometer is variable-resistor kind of device that enables mirror to actually "remember" the exact position -- just like the potentiometer for the sun roof. Potentiometer contacts may be dirty/worn/broken.

Unfortunantely, Audi don't supply mirror adjusting unit separately for cars with mirror memory function. The cost of whole unit for my car (4D2 858 531 BD 3FZ) is 315 UK pounds. I understand this doens't win the award for the most ridiculously expensive audi part, but still I'm not prepared to shell out this much.

I found a writeup about cost effective cleaning of potentiometers for Jeep vehicle, but couldn't find any writeup/info for Audis, though I've seen many posts about mirror return problem after the tilt function.

http://www.wjjeeps.com/mirrors2.htm#REPAIR

If anyone have experience of deep diving into the mirror insides please post here. Thanks.

[notorious]

RESOLVED. Writeup is below:

If your mirror doesn't return after tilting for reversing, the "potentiometer" in mirror housing is not clean or has a bad contact. "Potentiometer" is a combination of "female" copper element (number 1, see pictures below) based inside mirror housing and plastic "male" (number 2, see pictures below) which is part of mirror glass. As you might have guessed, male travels between female contacts back and forth (I'm sorry, I always think about sex), so the mirror electronics "knows" exact position of the mirror depending on position of male part inside female part. If you are interested in physics of the process, you can read this and this US patents.

If the system works well, you can move mirror glass with your hand or with joystick and then press and hold "recall from memory" button until mirror returns to remembered position. If contact is loose you can get all sorts of problems when it comes to remembering and recalling exact position of the mirror glass.

Solution:

1. Remove mirror glass. This is very easy. All you need is plastic stick. Don't worry -- you can't damage anything if your tool is made of plastic. Just pry it off -- the system is designed for easy removal of the mirror glass. Don't disconnect electric contacts unless you want to repair something else. All you need is to remove mirror glass so that it hangs on electric wires.
2. Clean plastic "male" if it's dirty.
3. Clean copper "female" if you see corrosion on it. Rub with sandpaper or with a thin file "inner lips" of the copper element where it contacts with "male".
4. Most important part. Take narrow pliers and squeeze copper element at the top and at the bottom. This will help copper "lips" to grasp the male part firmly from both sides. Don't press pliers too hard, as this will create excessive pressure on the male element. As a side effect of excessive pressure motors may have difficulty moving the mirror or you'll notice judder when adjusting the mirror.
5. Put glass back in place. It will just pop into place.
6. Sit into car. Adjust mirrors with joystick. Press Memory+1 to save current mirror position into memory. Move mirror with joystick or with your hand. Press button 1 until mirror returns back to saved position.
4. Start engine. Engage reverse. Mirror tilts. Engage parking position. Mirror returns. Problem resolved.

When you actually start doing this, you'll notice how easy and self-explanatory the procedure actually is. It will take from 30 minutes to 1 hour of your time.

P.S. I combined this procedure with installing "aspherical" mirror for passenger side, which is absolutely cool for observing blind spot. For my UK-based car with anti-dazzle feature the part number is "8D0 857 535 H".

[Conan_the_Librarian]

Top work fella. Good write up; added to the sticky. Thank you.

[Oli18]

Nice one Notorious and thanks for sharing!

[HPsauce]

Whilst not wishing to "rain on anyones parade" I do believe that the assumptions behind that repair process are incorrect.
If it did fix the problem it's probably purely coincidental and more likely to be down to the "reset" process described at the end, or just possibly by clearing a physical obstruction.

I am 100% convinced that the ONLY function of those metal contacts (and the plastic arc on the glass) is to stabilise the mirror, possibly reducing vibration.
As such they need to be clean and smooth and grip the plastic arc but not too tightly.

This is because in the last few days, as part of trying to fix a "folding" issue I have swapped and reswapped and tested thoroughly 2 different passenger mirror units on my S8.
Both have memory, support heated glass and do the "reverse dip"; the only issue is innacurate folding/unfolding (on both ).

So why do I think this?
Well the memory works fine, as does the reverse dip. With a little gentle "manual assistance" so does fold/unfold. On BOTH units.
Yet one doesn't even have the metal clips installed!

Furthermore the metal clips aren't connected to anything and are in fact ONE SINGLE PIECE OF BENT METAL held in place by a metal screw into the metal frame, so effectively earthed.
What's more swapping it between units made no difference to anything, both worked equally well with or without the clips.

So, that's my conclusion, hopefully it will help people consider the symptoms of their problems and not get confused when a published procedure doesn't actually fix the problem

-----------------------
Edit: I note that the mirror glass in the pictures above also has auto-dim which mine does not, although the wiring for it is present in the units (but not elsewhere in the car) - the plug is actually tucked away beside the fold motor in mine.

[Nollywood]

I'm with HP on this. I had a similar issue on my '96 4,2 QS. I bought a replacement unit, which worked fine. It had that clip, but it was a plastic one! So it wasn't the metal clip that was the issue.

[notorious]

Apologies for incorrect writeup. Described operation has helped me but I now admit my assumptions may not be correct as I didn't dig into the issue deep enough.

I had some experience fixing mirror memory issues on General Motors cars, which use potentiometers to "remember" mirror positions. Link: http://www.wjjeeps.com/mirrors2.htm Potentiometer contact become loose or get dirty so mirror "forgets" it's position. This is what mislead me.

As I will be swapping mirror caps soon and I will return to investigation of how mirror memory works on A8 D2s. It may use magnetic sensors to actually remember mirror position.


Edit: If mirror memory works properly I have discovered that it is possible to change position of mirror element by hand (even if car is fully off and locked). After car is opened the mirror will return to original position (with ignition or by manually pressing the "1" button -- I don't remember). This means there is a sensor (or two sensors?) in mirror housing that independently measure position of mirror element in space and gives feedback to mirror ECU.

[HPsauce]

There are definitely sensors there but I think they must be somewhere behind (or incorporated in) the adjustment motors. Exactly what they are I for one don't know.

No need to apologise, I found your writeup very helpful on how to get access.

Comparing them with, for example, the small headlight height adjustment motors on my ford Focus (similar vintage), those have the adjustment control totally built in and a very simple external connection into the sealed unit from the controller, which in this case is a wheel on the dashboard (variable resistance?).

[notorious]

HP, if you have a bit of time please read second patent (there are two links in my original write up). That second patent describes how mirror position can be "remembered" by just one magnetic corrosion-free sensor.

[HPsauce]

Had a quick look at both patents, very interesting.

However they were filed some years after my mirror was actually made.....