A6 C5 Quattro, 1997. I'm wondering if I can possibly diagnose and fix this without paying the garage, (repair shop). Started playing up yesterday, first off noticed the interior lights pulsating on and off when driving, then when I locked the car the alarm LEDs (the red LED by the window), was flashing faster than usual and sure enough the alarm triggered after half a minute or so.

Three doors and boot (trunk), operate the interior light and footwell lights as they should do, except the left side rear door which seems to have the sensor stuck to 'door closed', I'm fairly sure it was like that for a long time and didn't cause any problems. I'm having to lock the car by using the interior lock switch and exit by the passenger door for now. The CL works fine either by remote or key, and the interior lights work properly apart from pulsating on and off when driving.

I've checked the module under the carpet and its completely dry under there. Is there anything else I can do? Would dissing the battery for a few minutes be worth trying as a kind of reset function, in case some logic has gone funny?

I know you will say...Vag-Com, if I get access to one (ie buy a connector and lead for my laptop), how will I understand the error codes, is there a list of them I can look at somewhere?

Has anyone actually had this same set of symptoms and can say what it was causing it?

Any advice much appreciated, money is tight just now and I could do with finding a DIY solution .

 

My 1st guess is the left (left = drivers?) rear door latch.

2nd: short in lighting circuit, disconnect (left = drivers?) floor dome light. The one that lights up the foot well when that door is opened. It is located under the drivers seat, and is attached to the bottom of the seat. I don't remember which color it is, but I can look tonight and tell you.

3rd: bad drivers door latch

I had similar problems, my osc would tell me that the rear drivers door was open, and then closed, open and then closed. At the same time the interior lights would flash like I was at a disco. It turned out to be #2 above. Mine did not set off my alarm, so that is why I am guessing your problem is #1.

Best of luck,
Jeff

 

Thanks for your reply, its appreciated. UK model so left side is passenger here.

I did wonder about that rear door latch, though my thinking is if it is 'stuck in door closed' how can it be causing this problem? This rear door doesn't ever turn on the red door lights, foot well or interior lights when I open it, so I thought it would be out of the equation, I thought I'd be looking for the opposite latch fault, ie. door latch signaling 'door open' when in fact its shut. But I'm only using my own logic here and not any experience!

I'm reluctant to think any other door latch is at fault, because I can sit in the car with ignition off and the interior light does not come on, nor do any foot well lights, so no door is being detected as open, yet as soon as I start up the engine the interior light pulsates, (quiet slowly).

#2 sounds interesting and easy to check, its dark now, but tomorrow I'll disconnect this foot well light, rear left side and see if there might be a short.

Weird thing is, why does the interior light only play up once the engine is started? I'd have thought a faulty latch would be showing up symptoms either engine on or off. I think once the light fault is sorted the alarm will be working again too.

Thanks again, ideas appreciated.

 

If #2 is your problem, the reason the lights don't flash slowly (like mine did) when the car is off is because when you arm the alarm, the dome light circuit is shut off. If I lock myself in my car, arm the alarm, I can not turn on the map lights, the sun visor lights don't work and so forth. My lights only pulsed when I was sitting in the car and the car was turned on. Apparently, the weight of my body caused the wires under the cushion of my drivers seat to rub or something causing the short of the light attached the bottom of the seat.

While researching my light gremlins problems, I learned that the drivers door latch has some magical power over all the other door latches, so don't rule it out just because it doesn't make sense. Also bad door latches are very common on the c5 a6s and are very easy to change.

It is also possible that your rear door latch and the interior light issues are different. You have a bad rear door latch, and the foot well light under your drivers seat is shorting out.

Best of luck, if you can't figure out which plug is for the foot well light I can go outside and look.

edit: when the interior floor light shorts out, it tells the car that you have opened a door, causing the doom lights to fade on/off and possibly setting the alarm off. But mine never set my alarm off.

Jeff

 

Thanks for the explanations. I know I shouldn't trust my own logic here, (that might be faulty too), and when it comes to electric gremlins things can work mysteriously.

I'll go and investigate using your suggestions, if I have a problem identifying the right plug I'll get back to you.

I purchased a Vag-Com adapter yesterday, so maybe when I get that it will help...if it works!

The short on the floor light still looks promising, I'll have look and I'll let you know how I get on. Help is much appreciated!

 

I've got a Vag-Com connector this morning and had look at the CL module. Didn't take too long to work out what I could get information about. So, all doors report correctly when they are locked, unlocked and safe (safe meaning 'alarmed'), 3 doors also signal correctly when open, just L/H rear doesn't signal when open. So thats everything correct except rear door sensor stuck in 'door closed'.

I've disconnected the cable under the L/H front seat to the rear foot well light, and determined no short, or fault here.

I checked the fault codes and got his:

AG-COM Version: Release 409.1-S

Control Module Part Number: 4B0 962 258 B
Component and/or Version: Zentralverrieg.,DWA D28
Software Coding: 04750
Work Shop Code: WSC 02324
9 Faults Found:
01374 - Alarm triggered by Terminal 15
35-00 - -
01370 - Alarm triggered by Interior Monitoring
35-00 - -
01369 - Alarm triggered by Hood Switch
35-00 - -
01368 - Alarm triggered by Luggage Compartment Switch
35-00 - -
00956 - Key 2
09-10 - Adaptation Limit Surpassed - Intermittent
00957 - Key 3
09-10 - Adaptation Limit Surpassed - Intermittent
01560 - Passenger Door
59-10 - Can't Unlock - Intermittent
01561 - Left Rear Door
59-00 - Can't Unlock
01561 - Left Rear Door
61-00 - Won't De-Safe

The last two are because I disconnected the wiring to the that door, the first 4 faults I think are old, so I reckon the fault condition that is my problem is 0956/7, do they mean anything to anyone? I'm aware about the fault about not being able to unlock passenger door, intermittent, if I lean on this door it will open, though it is very rare that it does this.

I though now that I can read the reason for the alarm trigger I would set the alarm and after it goes off read the trigger code, but, guess what its not under the fault condition any more. Car has been locked and armed for over an hour and no alarm! I don't know whether to be pleased or not just yet.

So for the time being its OK, I haven't driven, but started up and the interior lights also behaving too. Did I disturb something?

If it comes back, any clues about what to look for with Vag-Com, and does anyone know how to disable the alarm if it comes to that?

 

So since disconnecting the rear seat foot well light the interior lights are responding normally now? No more flashing? Maybe the plug was a little corroded/loose and you seated it better.

If so then you just need to buy a rear door latch to get that door to lock/unlock normally again.

 

As partially expected I spoke too soon! Some intermittentcy now seems to be going on. You could well be right, I'm going to try and fix this rear door micro-switch and make sure that is working correctly before going any further, it could be a cause, or just a distraction, either way putting it right will be a good thing. It is locking and unlocking correctly, and going 'safe' correctly, it just is always reporting 'closed' and never 'open'. Of all the fault conditions it could get stuck in, this seems to me the least problematic, it shouldn't effect the alarm or central locking like this, but then again.

It's going to take a few more days off and on to work on it, so I'll update later on, just in case its useful for anyone with the same problem in the future.

Thanks again.

 

I suggest disconnecting the the rear door wiring harness that goes to the latch. Then see ff the problem goes away. If it does, the latch is one of the problems. If not, then there is a wiring short. Did you disconnect the rear foot well on the drivers side as well?

If the door latch and interior light issues are different, then the seat foot well short doesn't have to be limited to just the left side. It could be the right side instead.

 

OK I think its resolved thank you. Disconnecting the harness to the rear door and foot well lights didn't stop the fault, so I think red herrings.

I now think something got wet, not the unit under the seat that was bone dry. It had been raining very heavy for a few days leading up to this, and the day before it started I went through a flooded section of road, didn't register this connection at first.

So slowly the two faults cleared, a little intermittent to begin with, but now I can say cured, so I reconnected the door harness and the foot well light connector, and the faults still cured.

I can only guess that the flood I went through splashed up water and soaked some cables.

The outcome is I got a Vag-Com lead and really familiarized myself with the central locking module, I've also recoded it to change some of the options.

So thank you for your help and suggestions. I'm fairly sure now its fixed, it has behaved for long enough to feel confident to set the alarm again every time I leave the car, and no more interior lights coming on when driving.

Help was appreciated.