2005 Audi A6 electrical problem

No direct experience, but the general rule of thumb with faults of this type is to check all earth connections.

Undo any earth bolts or screws in the area, clean the metalwork back to bright, then reconnect.

Googling suggests it's a very common fault. In some cases it's suggested that the earth connection to the cluster is inadequate, and providing a separate earth connection will cure it. Others have needed to replace the cluster.

After that, I'm guessing this is a multiplexed car? As all the faults are in one area, it could be a module fault. You may need specialist help, or be prepared to fork out for parts to test with.

Chris

have you checked their operation with multiple bulbs on at the same time, as it may be a poor earth which overloads with several bulbs on together. and have you checked that the wattage of each bulb is correct (and of course that they are the correct bulb for the hole) Most lighting faults that I repair are user error, either wrong bulbs or wrongly fitted.

The bulbs are all (with one exception) those that came with the car two years ago, and the fault only started a week or so ago. The fault also happens without lights being used - turn the engine on on the drive way, leave all lights turned off and it will still do the same thing. The exception to the old bulbs is one that was changed about six months ago, so seems unlikely to go for almost six months before demonstrating the fault. Ive checked the bulbs are all as specified by Audi as well.

then all you can easily do will be to check and clean all the connections . For what it would cost in bulbs (compared to getting an auto electrician to look at it) it would be worth just replacing every bulb on that side with new, just in case.

Is there an electric control module around somewhere?. On Audis I've had I've sometimes run a soldering iron over the printed board where accessible and thats often cured rather odd faults..

There are a few Audi forums around on the net .. a post there might help..

There will be a module, but god only knows where. All that is easily accessible at the rear is the light cluster itself and the plug/cable to it. Nothing else is visible.

Do you have any water leaks/damp carpets?

The bulb detection is done by the Central Convenience or Central Electrics module (convenience, I think). One some VAG cars these are in a dubious position (the passenger footwell, for example), and they get wet, and corrode. Passats and the first Skoda Superb suffer with that a lot.

If you can find someone with VCDS to scan it, that might reveal some info.

some VAG had the module directly below the windscreen, subsequent to windscreen replacement it was ideally situated to get the possible resulting leak.

Its a common fault for these vehicles where the earth wire in the connecting plug is burnt out within the connector. Generally is caused by a high current draw.

It faults on the dash because of the computer or on board power supply module and has picked up a high resistance in the circuit.

You need to replace the bulb carrier the connector housing and the earth wire terminal. LHS

Hope this helps.

Why would they get wet in the passenger footwell? Unless the windscreen or whatever is leaking? It's actually quite a good place for electronics - better than under the bonnet where they get cooked.

I believe it's usually due to leaves blocking a drainage duct under the bonnet - with a secondary cause being leaky door seals.

But unless mounted in a stupid position, wouldn't you notice your feet getting wet before it reached the unit?

If it's like the Passat, it's not really mounted, just literally laid on the floor under the carpet. The carpet and underfelt are quite thick, and time-consuming to remove. It is entirely possible for the under-carpet area to be wet enough to damage the electronics, probably by the moist air condensing on the PCB, without the upper surface of the carpet feeling significantly wet.

Chris

No. It runs through the pollen filter, IIRC, down the bulkhead, and soaks the insulation (and the CCU) first, rather than dripping on you feet. The carpets get damp and the windows start to steam up all the time.

Thats correct - the unit detects that there is a high current draw.

But the problem has nothing to do with this unit or water or what ever. Its only detecting a tail lamp high resistance and throwing it up on the dash.

See my other post.

Low current draw, surely? High resistance, once the connector you mention has failed and the lights pack in?

Prsumably the connnector is a bit under-specced, gets hot, and fails?

Ah - right. I was assuming it was mounted on the bulkhead above floor level. Do they do other stupid things on this model?

In theory it's a good place to put it - many cars have ECUs bolted to the floor under the seats.

But it's not great when you get leaks.

yep