ABS Pump Replacement: Fix ABS/ASR/ESP Issues (V39)

Hello, I seem to have a serious problem with my car. I drove about 70 km non-stop twice over the weekend without any issues. Then the car sat for 2 hours, and I drove off again, but after about 50 meters, I heard a beeping sound, and the ESP, ABS, and the large warning triangle for the brakes all lit up. I tested the brakes, and they seem to be working, but the ABS, ASR, and ESP are no longer functioning. Then, after another 300 meters, I stopped and turned off the engine, restarted it, and drove off again, but all the lights were still on. I stopped, removed the key, and locked the car. Then I heard a humming sound in the engine compartment that I had never heard before. It was the ABS unit, which was still running even with the key removed. I disconnected the battery and went to Essen. An hour later, I reconnected the battery, and the ABS unit started running again, and I drove home for about 30 minutes. When I got home, the unit stopped running again, and everything seemed normal except for the warning lights in the instrument cluster. I then used VAG-COM to read the error codes:
Saturday, November 11, 2006, 2:49:37 PM.

VAG-COM Version: DRV 512.1-D
Control unit part number: 8D0 907 389 D.
Component and/or version: ABS/ESP front D36.
Encoding: 04255
Workshop code: WSC 00250.
"One error found:"
00301 - Return pump for ABS (V39)
35-00 - -

Okay, the error message is gone, the engine started, everything seems fine. I drove off, but after about 50 meters, all three warning lights came on again, along with a beeping sound. Then, the infamous pump started running again, and I decided to unplug that component until I could find the actual problem.

Okay, I wanted to know if anyone here has encountered a similar problem before and knows how to solve it.
Is the control unit (J104) included in this ABS module, or could the control unit be malfunctioning and sending incorrect commands to the ABS unit?

I am grateful for any information.

Thank you very much.

Okay, here's some news:

I obtained wiring diagrams to check the wiring of the hydro unit. After the car had been stationary for a week with the connector unplugged, and I was about to start working on it on Friday with the wiring diagrams, VAG-Com, and a multimeter, the error disappeared as soon as I plugged the connector back in – it was simply gone. I cleared the error memory and took it for a test drive, including ESP and ABS tests, and everything worked. I can hardly believe it. The week before (when I started this thread), I had plugged and unplugged the connector at least 10 times because I suspected a contact problem, but without success. Now everything is okay again, but I'm still concerned that the problem might return because I haven't found the actual cause.
When the error occurred, there was heavy rain, and I also got a lot of water splashed from the car in front on the highway, but that shouldn't have affected the car, especially since the error only appeared after a standstill of approximately 2 hours.

Hello.
Yesterday, I drove to work in my Audi, and there were no issues. However, on the way home (immediately after exiting the parking garage), the two warning lights (ABS and ESP/ASR) came on again, accompanied by a three-tone beeping sound. I immediately pulled over and unplugged the connector from the hydraulic block, as that pump then runs continuously when the error message appears.
So, I'm back in the same situation as I was last week, and I'll try to find the error this weekend. It seems like the problem occurs after the engine has been running for a while and is warm. When it cools down, the problem disappears again, as mentioned in my previous post. I might be able to reproduce the issue this weekend if the problem has gone away.

Tips are, of course, gladly accepted .

Thank you very much.

Hello,

I have two ideas:

a broken cable or a poorly crimped connection in the wiring harness.

or, even worse, a problem with the control unit.
Here too, a poor solder joint can be the culprit. When the device is warm, it expands, which can lead to contact problems. When it's cold, the circuit board contracts, the soldered joint makes contact again, and everything is okay.
That's a very nasty bug, and it's difficult to find.

Let's try to check the wiring harness first. If we don't find anything there, it's probably the control unit.

Best regards, Jochen.

Okay, this weekend I wanted to investigate the problem again, but as I suspected, the problem was gone. I simply plugged the cable back into the hydroelectric generator, and everything worked perfectly. I've left the windows open in the basement garage, hoping that any moisture, if present, will evaporate.
Let's see what it will be like tonight.
I'll try to locate the ESP control unit and hopefully find a fault there.

Okay, so, then it started happening again in the evening. All the lights came on again as I was trying to drive out of the parking garage (after driving 10 meters in first gear).
Okay, I've figured out that when there's a voltage (Ubat) present at pin 14 (gray wire) on the hydroblock connector, the hydro unit runs continuously. If there's no voltage there, everything works perfectly. So, there must be some component upstream that's malfunctioning and supplying voltage to this hydroblock, and it's not stopping until... eventually, it starts working again.

Could someone possibly provide me with wiring diagrams (the ones I've received so far unfortunately don't match my car) that show how the pins of this connector are wired?

It's an A4 Avant, 2.5 TDI, manufactured in 2000 (04/2000), equipped with ABS, ESP, and traction control. Based on my understanding, it should be a Bosch 5.3 system.
A gray wire must be connected to pin 14 of the water block (this was indicated as "ro/schw" on my diagram).

Thank you very much.

Okay everyone,

The problem has now been solved (woodworking...).

After repeatedly encountering the problem after extended periods of inactivity, I suspected there was an electrical short somewhere. But how could I find it without detailed wiring diagrams? Well, like in the old days, I started removing relays one by one until the problem disappeared. And sure enough, after 2 minutes, we found the culprit. Under the steering wheel, at the very back of the firewall, there's a relay holder, and one of the relays on it was faulty. It seemed to sometimes stick, causing the return pump to run constantly. We removed the cover from the relay, but couldn't see anything wrong. Without the cover, the relay worked fine for a week (until today). Just to be safe, we replaced the relay (it had the number 373 on it) with a different one, and since then, the problem has been gone.
I've installed the relay, which probably isn't working perfectly, in a way that allows me to access and replace it from the left side of the fuse box if necessary.

Thank you for your comments.

Hello.
I'm experiencing a similar problem with my Fabia:
Error message for ABS return pump: 35-00 - however, the pump is not running, and the two indicated lights are on.
Does anyone know if the relay for the pump in the Fabia is also called 373, or what its other name is and where it can be found?
A circuit diagram would be incredibly helpful in that case .
Thank you in advance.
Best regards,

Hmm, that already sounds suspicious. It's either a faulty relay (if there is one), or the fuse (which would also have to be "hidden" somewhere; it's a 40 or 50A fuse, so not just a small, standard one).
How did the problem arise? Did it happen suddenly, overnight, or while driving?