2000 Audi A8 2.8 - Faulty ABS control module
 

Hi guys ...

Hope you'll forgive me if I'm posting in the wrong section but it's my first time here.

Anyway, really hope someone out there can help ...

I've got an Audi A8 and some time ago, had some work done which involved the wheels being centred / aligned and the steering wheel being taken off to straight it up. Unfortunately at the time, the mechanic I used had trouble getting the steering wheel off and eventually, through brute force, ended up snapping a slip ring on the steering column.

Didn't think too much about it at the time; everything seemed to work, except for the airbag warning light being constantly on. However, a few other things had stopped working - the horn, and the ability to change up a gear via the steering wheel - so it went back to the mechanic for repair. Turns out the slip ring is also a wheel position sensor which feeds info the the ABS module, so it can determine how much braking effort needs to be applied to each wheel.

My mechanic has been having trouble with the slip ring supplied by his parts supplier but whilst this has been going on, he took it to a main dealer and the dealer advised that the ABS control module is faulty (it accepts input and new codes from the slip ring sensor but when the car is turned off and on again, the new codes have been wiped and the module won't 'talk' to the sensor).

I located a company on the Net that would rebuild an ABS module www.ecu-testing.com (main dealer wanted £1000 for a new ABS pump / module combination) and the mechanic sent the unit off for testing. They've received and tested the unit and contacted me with the words "we've tested your unit and there's nothing wrong with it - but there are no electronics inside the unit; there must be another control module somewhere else on your car" !!!!

Both the mechanic and I have queried this; there's a module, on the side of the pump, with a great big 9 pin multi-plug connector on the side of it, but they are absolutely adamant that what the mechanic sent is NOT the ABS control module and that there has to be another one somewhere else on the car, that will accept reprogramming !! :(

So, you can guess my question - has anyone got ANY idea where else the ABS control module might be on my A8 ?????? :confused:

I'd really appreciate your help / input, guys.

Thanks very much :)

It's a matter of terminology...Audi calls the entire "module" you sent off the "hydraulic unit"....most people call it the "Abs control module" and so do most repair companies.

What Audi terms the "ABS Control module" is located inside the cabin, under the instrument panel, mounted to the carrier (left side) above the pedal cluster. This is on a U.S. model 2000 A8 4.2, left hand drive.

Any programming or resetting of the ABS control module is done with Vag.com (or equivalent) through the main OBD2 diagnostic port, like all other control units.

P.S. The price of £1000 the dealer quoted you would be the normal (unfortunately) dealer price for the "ABS Hydraulic unit" under the hood ALONE and would NOT likely include the actual "ABS Control module" in the cabin.
When your mechanic had things checked, I'm assuming they correctly referred to the inside unit as the "ABS Control Module", which would be the only thing that would directly talk to the sensors...I have no idea about a price on that, or the likelihood of it failing on it's own. AGAIN, terminology all over the place, depending on who you speak with.
Many refer to the "ABS hydraulic unit" as a combo of hydraulic unit AND control module, as repair companies usually only need to repair the electrical half of that hydraulic unit...almost always the culprit in a failure of the unit (dealers only replace the hydraulic unit as a whole...NO repairs). The hydraulic half is not likely to fail unless fluid was contaminated with particulate matter. Anyway, at least you know that unit as a whole has been cleared as working correctly.

Additional info, if you didn't already know:

The ABS Control Module gets input from a lot of other systems, too. So an ABS light on the dash doesn't necessarily mean there's anything wrong with the ABS Control Module in the cabin. Only a diagnostic with Vag.com or dealer quality OBD2 scanner will determine that or another system that is tripping it.

The steering position sensor (among other sensors) also feeds input during any ESP (electronic stability control) event/correction (sliding sideways..."fish tailing", "plowing", etc)...assuming you have that system (standard on U.S. 2000 A8). This input is all fed into the ABS Control module, which in turn corrects the skid through the ABS hydraulic unit...braking one wheel at a time to correct/straighten the skid.