gbmarc

So the ABS light came on with the error code "ABS 00301 Return Flow Pump 27--00 Implausible signal".
I checked the pump fuse in the trunk and it was good.
Following another post I saw on the subject, I disconnected the pump, and tried running it directly by connecting it up to a 12v supply. It ran OK, although it didn't seem very vigorous - kinda half hearted, but then again I don't know what a new one runs like.

Any thoughts anyone?

123quattro

The hydraulic unit monitors speed of the motor and does closed loop control. I'd guess that the motor speed encoder is flaking out. Never seen the fault before.

silverd2

The most common problem with all Bosch ABS units is the module (black box on the pump unit).

One possible cause of that code is a faulty module "J105"

Dealers will replace the entire unit at upwards of $1500.

The module is repairable and replaceable for WAY less.

One rebuilder with a good rep...don't know if they are the cheapest though(?)

ABS Modules | Product Categories | ModuleMaster

PS: You can actually drive the car while the module is being tested and/or rebuilt by MM.

gbmarc

I've been trying to find the ABS pump relay J105 location but I'm getting nowhere. The wiring diagram says: "Relay panel under Driver's footwell"
but are they referring to a RHD or LHD car? There's relays under the right side kickboard but that relay panel doesn't look like anything in the wiring diagram. There are huge relays on a slide-out tray that doesn't really slide out because it's jammed in there with all the wires.
I've googled everywhere but can't find anyone who reveals the magic location secret. It's 20F in my garage and I'm slightly frustrated!

silverd2

???
Don't know what diagram you are viewing .... J105 is under the hood attached to the ABS pump >>> "black box on the pump unit"

gbmarc

This diagram:




Audi A8 ABS Wiring<br/>

gbmarc

I had the ABS hydraulic unit under the hood detached from the black part last week.
When separated the black box has the little piston actuators sticking out of it. Are you saying there's a cover that can be removed and that there's relays underneath?
The diagram below says it's #2 in the driver's footwell.

silverd2

Well, it seems Bentley says it both ways for all years. The component location in Bentley (I posted) indicates, I thought, that the relay is integral with the ABS "module" (black box) under the outside cover. Bentley may have gotten the terminology wrong and there is a separate relay under the driver's side (LHD).

I know the module is full of tiny solder joints that are prone to failure...the most common problem with Bosch ABS.

Is your car a 2000 USA model? Does it have ESP?

gbmarc

My car is a 2002 S8 with ESP.
I don't see any relays on the left side footwell (driver's side in my case) unless perhaps they are under the carpet on the transmission side. I had that carpet off a couple of months ago to check those red rubber water drains but I wasn't looking for relays then. I didn't want to remove it yesterday because I would have to fiddle with the gas pedal stop and the carpet never seems to go back in properly.

silverd2

Access to the secondary relay panel on the driver's side requires removal of the entire "knee panel" (not "storage" as Bentley says)under the steering wheel ... the panel the OBD port is mounted in. Many of the allen bolts are located under pry out trim inserts.

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