Heated mirrors/VCDS

[Topplumb1]

I have an A4/S4 B5 December 1999 1.8T Quattro Sport, passenger heated mirror works fine as does rear window heater, drivers door mirror has not worked for 4 years since I have had the car - only just realised they were heated ! Had the glass out and checked with a multimeter and it shows continuity on the glass element, swapped it with a new glass and same problem still does not work, I am wondering if it has been enabled? Maybe I need to think about getting hold of a VCDS diagnostic - I would like to know what you can do with a VCDS? I have read some forums on here that you can check, enable and disable modules, fault codes etc, would it be to my future advantage to buy one if anyone knows prices and where to obtain one from. I already have a basic fault code reader but is very limited as to what it can do.


Thanks.

 

[a3tdi2001]

Before you hit VCDS. Does the mirror have a thermoswitch on the rear side of the glass?

 

[Topplumb1]

On the back of the mirror when you hold it with the 2 electrical connections at the bottom left corner - at the top right corner is a round raised part with a silver disc beneath it touching the glass through the plastic - could this be a thermoswitch?

 

[aragorn]

The mirrors arent controlled electronically, they're just powered all the time.

Check if your getting 12v at the feed wire.

 

[ScottD3]

vcds Is a bit limited on the B5s, most of the coding and options is in the cluster.
there is some options in the engine ecu and auto box ecu but nothing for the mirrors.

you might need to get back to good old fashion wire hunting.

 

[Topplumb1]

Aragorn : There is a 12v supply showing on my multimeter when you turn the ignition on and off at the mirror terminals with the mirror removed.

 

[Arrkon]

must be a reason for it... you say you checked the glass and the wiring... doesnt leave much else

 

[a3tdi2001]

On the back of the mirror when you hold it with the 2 electrical connections at the bottom left corner - at the top right corner is a round raised part with a silver disc beneath it touching the glass through the plastic - could this be a thermoswitch?

Yes that is most likely the thermoswitch. If they are similar to my A3 mirrors then they only operate below 12 degrees C when working properly. An easy check is to measure the resistance across both terminals at room temperature, should give infinite reading, and then again after placing them in the fridge for a bit. A cheap fix is to solder a piece of low resistance wire across the thermoswitch to bypass it.

 

[ScottD3]

is there a earth?

 

[Topplumb1]

I the thermoswitch is dodgy......so I have ordered a new glass off ebay, should be here in a couple of days......I will post a message on here if it cures the problem.

 

[Topplumb1]

So people......new mirror glass arrived today, fitted and hey presto the drivers door mirror is now fully funtional and working correctly - thanks for everyones help

 

[Nessy]

The mirror glass IIRC was permanently heated on the earlier models of A4, which is why the mirrors are so often burnt out now the cars have got so old.....
The later ones are defo controlled by ambient temperature, below 12C sounds about right, some have mooted 5C as the set-point but mine defintely heat up at ambient temperatures warmer than 5......
My '99 pre-facelift mirrors are stone cold normally , once it gets nippy tho' the mirrors instantly heat up, opening the window and feeling the mirror glass you can really sense the warmth.
That leads to one of the few things I dislike about the car though, in muggy and mild wet weather the mirrors don't clear as it isn't cold enough for the heating elements to operate.
My old 80 Avant had permanently heated mirrors and it was a much safer state of affairs IMHO.