Brand new heated wing mirrors failed after 30 minutes!!

Just got two brand new mirrors from Audi to replace both the passenger side (no longer heating) and the drivers side (heating, but has a rusty mess under the glass).

I fitted them and checked that they were heating up when the ignition is on (my pre-facelift S3 permanently supplys 12V to the mirrors when the ignition is on) - they worked fine. Then I took a short trip to the shops and when I got back I checked them again and they were stone cold!

At first I thought maybe they only operate during the first few minutes of switching on, but now I've checked the fuse, and had the mirrors off again to find amazingly that both mirror elements have failed. I've checked this with a multi-meter, the old working mirror has ~20ohms across the contacts where the new mirrors are open circuit. Sure enough re-connected the old mirror and it works fine.

Needless to say the ones I bought will be going back, but surely this is likely to happen again with any replacements. Is there anything I could have done differently to avoid this?

Oh, and I did check the part numbers and the old and new match exactly. Reckon I'll be "running in" any new ones with a 12V power supply for a while before I bother to fit them whether that will make any difference.

S3 Rav said:

How much were they from Audi mate?

Click to expand...

Can't rememebr exactly now but around £30+ for the passenger side and around 45 for the drivers because of the blind spot mirror. Not exactly cheap for two bits of glass, even with a heating element stuck to the back.

NHN said:

Thats fairly unheard of tbh, never read that, chances of frying the tracks if oem are remote, must have been some current going through them to kill.

Click to expand...

Agreed that's why I'm a bit confused. No question about it though, I switched between them a couple of times now.

jojo said:

They only work when it's cold enough outside IIRC, as they have a built in thermostat

Click to expand...

Only post facelift models as far as I read elsewhere. I've checked the voltage across the wires and its 12V as soon as I turn on the ignition, and its not exactly very cold outside.

I've had to book the car in now to get this sorted, as the parts dept won't replace them once they've gone on the car. Should be warranty job though.

a3tdi2001 said:

I had a look at my glass today. The thermoswitch is positioned behind the glass itself at the bottom outermost corner IIRC, looks like a large watch battery inside the black plastic casing. So yes they will switch off and read infinite resistance after they reach a set temperature. You could test by holding an ice cube down over the thermoswitch with the ignition on and see if they come back on. They probably will with them being new. I'm hoping that a broken heater can be repaired by bridging a wire across the thermistor so that they are on all the time and will post once I try and repair my one.

Click to expand...

Hmm, I had thought that cylindrical thing (on mine this is actually in the top corner nearest the car, the connectors are in the opposite corner) was involved in the heating somehow but if you're right I still don't understand how they went hot when I first put them on. I suppose the reason for my original one always heating up might be a faulty thermistor as they were at the same temperature when I was swapping between. So I guess you can't really test the mirror glass on its own unless you cool it first. I'm off to put one in the freezer now...

If you're right then I've been misled by another post I read that said pre-facelift ones were always on, plus the fact that my old one was behaving differently.

Yep the old ones have the lump too.

Just measured the resistance on the new ones after being in the freezer - 0.04 ohms. I'm assuming it will work under this condition on the (will check tomorrow). Thanks for the tip - I would have looked a bit dumb taking the car in for this!

Should've waited till winter to replace them.