Auto darkening mirrors
 

Hi guys. now that my starting issues are resolved its time to get down to fixing the other annoying niggles that the car has.

One of these is that the driver's side auto darkening mirror very often auto darkens - and stays dark, meanwhile the rear view mirror stops working altogether. The passenger side is not affected due to being a non - darkening replacement.

The problem always occurs on start-up and as far as I can make out can only be fixed by pulling the battery for a few seconds. I originally thought it was due to the car struggling to start and causing various electrical glitches but it has since done it with the fixed starting.

So for the questions: Has anyone experienced this before/know what causes it and know how to stop it happening or even how to reset them without pulling the battery?

I'm slightly suspicious of the power management module. It doesnt communicate with my crappy copy of VCDS so I cant see if it has any faults logged. It seems the auto darkening mirrors are expensive to replace and there is something of a waiting list for them! I would really like to replace both the wing mirrors though as I constantly get dazzled by the passenger side one and the liquid inside the drivers side one leaves a little to be desired.

gill

I'd disconnect the drivers side one and see how the system behaves; it could have a fault that is throwing the control module off?

Its worth a try. I should have mentioned that there are no faults logged on VCDS fo the mirrors. when the drivers side mirror goes dark the rear view fails to go dark.

My suspicion is that it is some sort of voltage spike type fault due to it only happening when the engine is starting, but that is purely a suspicion. Its one of those faults that is a niggle, but an annoying niggle all the same haha.

How clever are the dimming mirrors in a D3? I suspect the answer is "not in the least" but I don't know the setup.

Most systems are remarkably simple - a sensor (usually two, one for daylight, the other for detecting headlights behind) in the interior mirror and a very simple control circuit that varies a voltage to all 3 mirror glasses (interior, left and right) to control the dimming.

So just replacing the interior mirror unit may fix it. £26.59 from our sponsors: http://www.ebay.co.uk/itm/Audi-A8-D3...-/170928366722 ;)
I'm sure other colours are also available if that doesn't match. :D

Of course, as you probably know, the exterior mirror glass is in a separate price category. :tuttut:

Are the interior mirrors the same for the D2 and the D3? They certainly look the same. I have a D2 one sitting around already.

I will wait and see if it continues doing it before I start taking bits apart. It has only done it the once since the starting problem was sorted.

Ok, so this is getting annoying now. It is consistently below freezing every morning up here now. This takes more juice from the battery to start it which seems to be what is causing the fault with the mirrors. I will try changing the rear view mirror and see if that makes any difference seeing as I have one (D2 though).

I wonder if the keyless entry is draining the battery overnight enough to cause the problem. I wonder if the countless jump starts and battery drains from the hot start issue I used to have has damaged the circuitry?? There are so many variables for what should be a fairly simple system its bordering on alarming!

Just an update. Wing mirrors still going black/rear view not working on just about every cold start. Still work after battery disconnect.

I took the roof mopdule apart so that I could get the mirror off to try the D2 one. Although externally the mirrors are identical the wiring and plugs are different so that was a non starter.

Given that there are so many wires going between the mirror and the roof module, Im dubious that changing the mirror would make any difference. I suspect its all controlled from the roof module.

I'm going to see what the CCA rating on my land rover battery is and if its suitable I will try it in the D3 and see if its any better. Can try the one out of the D2 as well, its sitting on a trickle charger in my workshop. If it stops the problem then I will buy a new 900/1000 CCA AGM battery.

If I cant find out what the problem is I'm tempted to disconnect the mirror altogether and fit the manual one from the D2. There are so many people driving around with fog lights permanently on, plus super bright LED/xenon headlights combined with hilly country roads and a 26 mile commute that I cant deal with the dazzle if the rear view isnt working. I can deal with the wing mirrors going dark, but the rear view is a nightmare hence the twice daily battery pull.

Auto dim mirrors in the D3 are controlled by the roof module.

They are prone to water damage if you have a sunroof

Checking it for errors would be a good start.

You can also check the measuring blocks to see how bright the car thinks the lights behind are and thus how much dim it should apply.

Worst case the dimming mirrors can be coded out from the roof module completely and they shouldn't ever dim again....

I wouldn't expect any interoperability between D2 and D3, even if there are visual similarities. They are over a decade apart design wise....

I dont have a sunroof, so can rule that one out at least.

I have tried looking for errors/fault codes, but I cant find any mention of them at all in VCDS. I can find heated mirrors but no auto dimming. No errors for them come up in auto scans. VCDS didnt run very well on my little windows tablet (no communication with the majority of modules) It works better on my big laptop, although that is what I used last time and still couldnt find any mention of the auto dimming mirrors.

Checking measuring blocks for how bright it thinks the lights are (assuming I could find them in VCDS) wouldnt achieve much as they work perfectly when they do work.

Coding them out altogether is not an option as the problem is the dazzle from drivers behind in the rear view - it's only the wing mirrors which darken permanently (when in fault), the rear view stays bright.

This only happens when starting the car from cold. To me it seems like the starter is drawing so much from the battery that the voltage supplied to the roof module is reduced causing the fault.

i dont know whether the power management module is meant to prevent this and is therefore at fault, or how to test it. It may be that the battery itself is knackered. With the starting problems that i had, the car was getting jump started pretty much daily, and turning a dead engine for ages at a time until it caught so it could well be FUBAR. I have two batteries for it, and they are both much the same.

I checked the battery in the land rover last night and it is 850 CCA. not as much as I'd like, but it should do to test the battery hypothesis. After that I suppose I can only really try the shotgun parts technique and change out the roof module and try that, if not, the the battery management module would be my next guess. Guessing however is as good as it gets at the moment.

Worst case scenario, I'll fit the manual rear view out of the D2. It will mean no ambient lighting and no map reading lights (different wiring connectors) but I can at least flip the little tab at the bottom to darken the mirror when Mr I-dont-care-if-its-not-foggy-I'm-driving-a-corsa-and-am-therefore-better-than-you-and-Im-going-to-blind-you-with-my-foglights-like-a-**** is driving right up my tailpipe looking like a spaceship.

gill

Is the current battery a genuine VAG one and is it coded to the car?