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Audi A6 brake light fog light interaction
matt_gsxr - 17/7/13 at 09:11 AM

Hey there,

Just got my 2005 Audi A6 MOTed. It got through fine but with a question mark over the brake light operation.


So,
There are 5 areas that light up under normal operation.
1 in the rear screen
1 on the inner right
1 on the outer right
1 on the inner left
1 on the outer left.
These all operate fine when the fog-light is off.

With the rear fog-lights on
Only the rear screen and the 2 inner brake lights operate.

It is all symmetrical so I doubt it is earthing related, which was my first guess.

They gave it a pass because the brake lights worked, but they weren't happy.

Anyone got any experience of this. It is a very early version of this car (54 plate). It has been through loads of MOT's previously with no mention. I haven't messed around with it (as far as I remember).

I don't think I have ever used the rear fog-light, so it is a bit academic, but its in my head now!

Matt


Slimy38 - 17/7/13 at 09:21 AM

Actually, I think you were right the first time. In some cases, the 'centre' lights (IE the rear screen and the inner lights) come off one earth, and the outer lights come off another. It's usually related to the wiring diagram for a hatchback, IE the ones attached to the tailgate are all in one circuit, and the ones attached to the car are a second circuit.

It sounds like the fog light (that I'm guessing is in the 'outer' cluster?) is causing an earth short.


matt_gsxr - 17/7/13 at 09:26 AM

fog light is in the outer cluster.

Electrics on this car are mega complicated.
I was really hoping someone was going to say that this is what its supposed to do!


AndyW - 17/7/13 at 10:44 AM

quote:
Originally posted by matt_gsxr
fog light is in the outer cluster.

Electrics on this car are mega complicated.
I was really hoping someone was going to say that this is what its supposed to do!


That's what I was going to suggest, if the fog light is in the outer cluster, it would make sense that when the fog lights are on, that the brake light on the inner cluster work only, this would stop the outer brake light becoming masked by the fog light. These cars are immensely complicated and do things that we are not aware of!!!


matt_gsxr - 17/7/13 at 03:27 PM

I'll post something on the vwaudiforum to see if it is normal behaviour (I hope it is, but I am not optimistic)


FuryLee - 19/7/13 at 06:32 PM

Hi Adrian has asked me to comment on the opporation of A6 rear lights. Ca'nt think why he asked me!

The lights are opporating exactly as they should, just as any kit going through IVA have to have a specific gap between the fog and stop lights, all european manufactures have to abide by the same rule.As has allready been sugested, Its purpose is to clearly show when the stop lights have been applied in all conditions.

Lee audi master tech


britishtrident - 19/7/13 at 06:45 PM

All getting too clever by half.

Today I rectified an engine warning light on a Nissan Note the cause was a defective reverse light switch --- for anybody with a Nissan who might be interested the fault code was P1706.


matt_gsxr - 19/7/13 at 09:17 PM

quote:
Originally posted by FuryLee
Hi Adrian has asked me to comment on the opporation of A6 rear lights. Ca'nt think why he asked me!

The lights are opporating exactly as they should, just as any kit going through IVA have to have a specific gap between the fog and stop lights, all european manufactures have to abide by the same rule.As has allready been sugested, Its purpose is to clearly show when the stop lights have been applied in all conditions.

Lee audi master tech


Thanks Lee.
Thanks for clearing this up.
I'll print this out for the next MOT (or probably just take it somewhere else).

Thanks again,

matt