ABS Error: Control Unit Not Responding

Hello everyone,
My first topic, and already a somewhat difficult question:

I have an ABS system malfunction in my Passat V6 TDI, model 3B, manufactured in 1998.

Either I get an error message immediately after starting the car, or it appears suddenly while driving, and of course, in that case, the navigation system also stops working (the route is no longer updated).
What makes me suspicious is that the ASR warning light occasionally illuminates, and then the ASR switch becomes non-functional.
Occasionally, these warning messages also disappear even when I drive the car for a longer period. Then, everything seems to be okay, and brake tests also indicate that the ABS and ASR systems are functioning.
The VAG workshop tried to read the error codes, but couldn't connect to the control unit, which suggests a fault there.

What other components could potentially produce a similar error pattern?

I'm a bit hesitant to spend the money on having a new control unit installed just to see if it fixes the problem. Besides, VAG (Volkswagen Group) won't take back the components afterwards.

I had the wiring diagrams printed out and I wanted to test the control unit, the contacts, and the accelerator pedal sensor.
Unfortunately, I still can't find the control unit. (According to the wiring diagram, the control unit should be located in the footwell on the right side, and the sensor should be under the rear seat, but there was nothing there.)

Perhaps someone can help me or has experienced a similar problem before?

hi.

I chose the 1999 model year because I can't find a V6 TDI engine for the 1998 model.

There are different possible installation locations.

ABS control unit:

either under the carpet on the passenger side, near the firewall, or...
directly at the (auxiliary) hydraulic unit in the engine compartment.

accelerometer (for lateral acceleration)

either under the rear seat or...
under the carpet (-> remove the driver's seat and rear bench seat)

Thank you for the information.


I can't access the circuit board on the pump because it's too tightly installed.

And I'm going to look for the lateral acceleration sensor today.

Hello Ignorabimus,
I've been experiencing the exact same problem with my A4 (B5) 2.5 TDI (AFB) from March 1999 for about two weeks now, and unfortunately, I haven't been able to identify the cause.
Were you able to fix the problem in the meantime? And if so, how?

Hello,

Yes, I have found the solution to the problem.
It was the control unit that was mounted on the hydraulic unit.
The error seems to occur more frequently in this version, so Bosch is addressing it.
The repair kit includes only the electronics, but not the hydraulic unit.
and costs approximately 500 euros.
The repair is very simple. Remove the pump assembly, then remove the 4 screws.
Remove the electronics, including the 12 solenoid coils, and replace them with the new ones.
Unfortunately, this sentence is not easy to understand. However, I received it from an electronics company in Bochum and installed it "at my own risk."
After that, the controller only needs to be programmed at a Bosch workshop so that it knows which engine and transmission are installed, and then it will work again. The labor time is approximately 1 hour, and the cost savings are approximately €700.

Ignorabimus wrote:

Unfortunately, this sentence is not so easy to translate.

You can get it at any VW dealership, and it costs approximately 490 EUR.

I'm experiencing a similar problem with a 1998 A4. The error code indicates a "control unit defect." I'd like to know if the hydraulic block needs to be removed in order to access and detach the control unit. Will brake fluid leak out when the control unit is unscrewed?