Comfort control unit differences? A6 4B

Hello,
This is my first post here in the forum; until now, I have only read posts.

The interior lighting in my Audi A6 4B 2.5 TDI (year of manufacture 2003) is malfunctioning.
The driver's door and rear doors, including the trunk, are all working fine, but the passenger-side door is having issues. When the ignition is off, the door opens, the interior light turns on and stays on for about 10 seconds, then it flickers briefly before staying on.
When the ignition is turned on -> The door open light flashes intermittently, the passenger door is not recognized by the instrument cluster (FIS). The front footwell lighting does not work at all, the warning chime for the open door when the lights are on also doesn't sound, and the manual central locking system also doesn't work.
The passenger-side microswitch has already been replaced... no change. The cables have been checked - nothing was found to be wrong.
My guess is that the central locking control unit (comfort control module) is faulty. If the interior light is flashing, it's likely making a clicking sound inside the control unit in sync with the flashes.
Now, there are different part numbers for the control units, and the last letter is different, for example, 4B0962258L and 4B0962258D.
Does anyone know what the difference is in the control unit? Is it a different programming or something else?

I'd like to try replacing the control unit to see if that's the problem, but I can only find ones with the "L" designation for over €140, and that's too expensive for me just to test.

Error memory was read -> no entry found in the control unit.

Hi,

I've probably written this a billion times: the letter is part of the part number, and if that letter is different, it's a different part. Also, it depends on the correct coding of the control unit, which usually requires using VCDS.

Best regards, Rainer.

Hi there.

Check if the KSG (Kühlsystemgeber) is submerged and inspect the supply line towards the water pump; I'm familiar with these issues from various Passat 3B and 3BG models, which are technically similar to your Audi.

The KSG was just outside yesterday for the part number check, and everything was dry!
Is a standard multimeter sufficient for checking the wiring? And what's the best way to do that?
I'm not very good with electricity... anything that has more than three wires is dangerous .

Remove the makeshift insulation from the wires and check if there are any exposed sections.

What does the error memory say?

Before you start, you might want to disconnect the battery for a moment. Sometimes, even if the KSG (Kurbelstromgenerator) isn't flooded, it can still malfunction.
If the microswitch or door lock have already been replaced, a broken cable in the area between the door and the body is a common issue.

Error memory is clear. I'll test the battery later.
I've already removed the rubber boot on the passenger-side door and checked for any exposed wires, but I didn't find anything.
I'll take a closer look at that again.
"Could this be related to the malfunctioning footwell lighting and the warning chime in the instrument cluster?"

I found the bug.
The cable harness in the passenger footwell is soaked.
"A cap in the floor panel is leaking, which has caused the carpet to..."
soaked with foam.
Three interconnected cables were corroded, I reconnected everything, and sure enough...
Everything is working again: the interior lights, footwell lighting, warning buzzer, and the FIS (multifunction display) now recognizes the passenger door again!
Now, all that's left to do is address the rust in the footwell.

Thank you for the feedback!

Sure, you're welcome!
It annoys me when threads just fizzle out without any result.

As I said, it's a known problem. If the copper worm is present, you can identify it by the brownish discoloration of the copper. Then, it needs to be cut out like rust or cancer, all the way down to the "healthy" material.

Hello there.

I've been searching for a solution to my problem for what feels like an eternity, and I was about to give up when I found your post.

Okay, I have the exact same car as you: an Audi A6 4B Quattro 2.5 TDI, with the BHD engine and a manual transmission.

"I'm experiencing the exact same problem you had: no display in the Driver Information System (FIS), a brief flashing of the overhead lights and door lights, and no footwell lighting, all on both the driver and passenger sides. Everything else seems to be working."

I've already replaced the lock and also bought the very expensive control unit, and I've even replaced the wiring harness for the door, but unfortunately, it hasn't worked.

I've now exposed the cable insulation again and lifted the carpet. Fortunately, everything is dry in my case, but there's nothing visible on the cables themselves.

Okay, and now for my question to you/you all =).

Could you possibly tell me the colors of the wires that were connected and which ones you reconnected? I'd like to trace them back to the central locking control unit, as there might be a break somewhere else in the wiring. If I find another break, I'll replace the entire cable run. Do you happen to have any more photos of the connections, or any tips or experiences related to this issue?

"Does anyone have the pinout diagram for the door control unit?"

I'm feeling quite desperate =(. I would be very grateful for your help!

Best regards,

Hi there,
Before you proceed to work on the control units, a vehicle scan would be quite helpful.
The errors don't necessarily have to be stored in the comfort control unit.
What happened before? Was it a random error or did something change?
You can find the wiring diagrams and fuse assignments (!) in the electrical schematic for your vehicle type.
You can find it for a few tens of euros along with other repair guides tailored to your vehicle, available online at Erwin (from Audi).
hg
Herbert.