Coupe Autocheck light warning. Help.

wildoliver · 16-11-12, 09:01 PM

I have a problem on the coupe I have dragged back on to the road. 1991 2.3 20v Quattro.

Firstly this car has been so full of bodges it's scary, the seller was a complete cowboy, lied about the condition of the car (quite blatantly actually).

Electrically it's a mess, the autocheck keeps throwing a warning for light bulb out when side lights are activated, it is only side lights that throw this warning, I've tested the autocheck unit against a known good unit so I know it's wiring somewhere.

I suspect the problem may lie in the rear lights, not least because as well as the main plug on to the rear light back boards there is a seperate wire on both sides which goes nowhere, it's an original loom wire that actually looks to match the side light wiring too but has a bodgit connector tagged on to the end definitely not original Audi.

So my question is how to track down this fault or disable the light section of the autocheck, either will do but it would be nice to keep the feature.

Many thanks

Oliver

missfire · 16-11-12, 09:23 PM

All of mine do that, all the time, whether the lights are on or off, and all of the lights work fine.

I read somewhere that it's triggered by resistance imbalance, and that even different brands or types of bulbs on either side can set it off. Don't know if that's right though.

mikes2 · 17-11-12, 12:09 AM

The sidelights are not part of the autocheck system, at least they shouldn't be.

You should be able to remove the sidelights completely and not trigger an autocheck warning. The current they draw is low enough not to be detected.

It might be dim dip related though. When your sidelights are on, the H4 bulbs are also used on a dim setting to provide additional lighting. There's a dim dip relay under the dash - it's usually pink. There's also a heavy resistive wire in the circuit - think it's under the carpet.

Error404 · 17-11-12, 12:14 AM

you can disable the dim dip by removing a pin at the headlight switch - I'll see if i can dig out a pic

wildoliver · 17-11-12, 06:39 PM

Excellent thanks chaps.

I'll check the headlight bulbs to make sure they are right, then look at the relay, looks like I've got a fun day tomorrow!

Still it passed MOT at least, the bodges are mostly gone, the marks of previous moron owner mostly gone and it's starting to turn in to a decent car.

Just need a set of shocks for it now and I think it's there mechanically till I start on the front end of the engine.

msh · 17-11-12, 07:25 PM

The principle is simple - if the warning pops out when you turn on just side markers [I guess that's "sidelights"

] then the problem is in rear lights. If it doesn't and it pops out when you turn on low beams, then the problem is in front.

AFAIK that hella system measures voltage drop to test bulbs, that's why always it is required to push brake pedal to get rid of brake light warning.

17-11-12, 12:09 AM	#3
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	The sidelights are not part of the autocheck system, at least they shouldn't be. You should be able to remove the sidelights completely and not trigger an autocheck warning. The current they draw is low enough not to be detected. It might be dim dip related though. When your sidelights are on, the H4 bulbs are also used on a dim setting to provide additional lighting. There's a dim dip relay under the dash - it's usually pink. There's also a heavy resistive wire in the circuit - think it's under the carpet. __________________ 1991 90 quattro 20v sport 1991 90 quattro

16-11-12, 09:23 PM	#2
missfire making wooden things Classic Audi Club Member Join Date: Dec 2009 Location: cow land Posts: 8,156	All of mine do that, all the time, whether the lights are on or off, and all of the lights work fine. I read somewhere that it's triggered by resistance imbalance, and that even different brands or types of bulbs on either side can set it off. Don't know if that's right though.

17-11-12, 12:14 AM	#4
Error404 Thobbing Member Classic Audi Club Member Join Date: Sep 2008 Location: Staffs Posts: 490	you can disable the dim dip by removing a pin at the headlight switch - I'll see if i can dig out a pic

17-11-12, 06:39 PM	#5
wildoliver Grown up member Join Date: Feb 2009 Posts: 436	Excellent thanks chaps. I'll check the headlight bulbs to make sure they are right, then look at the relay, looks like I've got a fun day tomorrow! Still it passed MOT at least, the bodges are mostly gone, the marks of previous moron owner mostly gone and it's starting to turn in to a decent car. Just need a set of shocks for it now and I think it's there mechanically till I start on the front end of the engine.

17-11-12, 07:25 PM	#6
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	The principle is simple - if the warning pops out when you turn on just side markers [I guess that's "sidelights" ] then the problem is in rear lights. If it doesn't and it pops out when you turn on low beams, then the problem is in front. AFAIK that hella system measures voltage drop to test bulbs, that's why always it is required to push brake pedal to get rid of brake light warning.