Defective Door Lock Control Unit?

Hello everyone,

My A6 4B (model year 2000) is slowly driving me crazy. And while searching for help, I ended up on this forum; unfortunately, the search function didn't return anything relevant to my problems.

"I lock the car using the Facebook app, and after a few minutes, all the turn signals come on (not blinking, but constantly lit) until the battery is dead the next morning. If the car is parked in the garage, you wouldn't even notice anything."
Now I've pulled out the fuse for the hazard lights.

Then even more great things happened.
"If I want the turn signals to flash now (whether with or without the warning light relay), they flash very quickly, as if two out of three bulbs on one side are broken, but they aren't."

"When I get into the car, the instrument cluster display shows that all four doors are open, but not the tailgate. If this is the case, I also can't manually turn on the interior lights, and the power windows don't work either."
Then, during the drive, the interior lights turn on for a few seconds, the door symbol disappears from the instrument cluster display (FIS), and the power windows and interior lights start working again, but unfortunately, the turn signals still don't work.

I've already replaced the turn signal relay twice, but unfortunately, that wasn't the problem.

Given that the interior lighting and window mechanisms are completely deactivated after locking with the remote control, I suspect that the issue might be related to the central locking system's control unit, as it also controls the turn signals in a way.

Is my control unit flooded or defective? Is the device actually located under the carpet on the driver's side, right where the driver's foot rests while driving?

Thank you in advance for any advice you can offer.

Regards,
Tobi.

My tip:

Connect to the diagnostic port (OBD-II), use a VAG-COM device, and check the door contacts. Let's see what information becomes available then. Otherwise, you usually can't figure out these kinds of electronic issues.

You've probably already checked for obvious things like damaged wiring harnesses, right?

The cables in the doors are okay.

I have an old VAG-Com device that doesn't support the CAN bus yet.
Some control units appear to be connected to the CAN bus in a way that seems "normal."

Because my car is from a period before the official introduction of the CAN bus system, but still has some features like navigation, it can sometimes be tricky.

Someone told me that the 2.5 TDI with 132 kW apparently had this issue before, but it didn't appear in other models until one or two months later. Maybe that's true.

This prevents me from accessing all the control units or reading out error codes.
It's related to the climate control and the engine, but not the all-in-one device.

Unfortunately, the IT department was also involved in that issue. I will try again today.

Regards,
Tobi.

Hello.

Have you checked ALL the fuses?

I had a similar problem with the car's electrical system. After searching for a while, I found out that the fuse for the interior lights was defective. I replaced the fuse, and then three other problems resolved themselves at once. That didn't seem logical to me.

Best regards, Ninja.

While the Audi A6 (4B) has an extended CAN data bus network starting from the model year 2000, this is not related to diagnostics. For this specific model year, diagnostics are explicitly performed via connector K1; neither connector K2 nor the CAN bus are used for diagnostic purposes.

If you still cannot establish a connection to all control units, make sure that your interface hardware is not the cause. Otherwise, as my predecessor mentioned, check the power supply in both directions (ground and positive).

Okay, thanks for the responses!

I was actually able to read the control unit data, and I saved the text somewhere on my laptop.

But all of that became irrelevant later because the device simply flooded (the HVAC control unit). If you know where to look, it's obvious that if there's moisture in the car, water will eventually end up somewhere (in my case, an estimated 4-5 liters in the driver's footwell from front to back!!). It's not a submarine, after all.

Okay, seat out, rug out, box out, thoroughly dried, old cables reattached, and everything cleaned up – now it's all perfect!

It took me two days to find the hole through which water had entered the car. The seal between the engine control unit and the interior wasn't completely watertight. It's quite a cost-saving measure to use such a flimsy seal that is supposed to be sealed with two screws in a plastic housing... Oh well, I just put some silicone on it and fixed it.

Regards,
TundB