Help! ABS related fault codes B6 S4

[re2500]

HELP! I know this isnt a b4 platform car, but i know there are some pretty handy people on the forum when it comes to electrical systems, so i'm hoping someone can help.
Unfortunately ive come across a little electrical gremlin in the new b6. I'm having an intermittent issue that im sure is related to the ABS system.
Car: 2003 B6 S4 4.2 Avant

The symptoms are as follows:
- The error either occurs on startup or can appear mid journey, it can also happen that it disappears mid journey also. Ive had it come and go up to 4 times in 10 miles. Or not happen at all for 30 miles.
- The car beeps several times with the Computer module showing a large red flashing “ (!) BRAKE “ and the red (!) light flashes also.
- The ABS light is illuminated
- The TCS light is sometimes illuminated, but not every time.
- The Speedo or Odometer is not working
- Sometimes but not always the steering feels heavier at lower speeds.
- Rear parking sensors will not operate during fault condition (this is an observation, but not sure how it is related)

I have a handheld OBD code reader so I have searched for codes whenever the fault appears to try and find a trend of some sort.
I get the following codes regularly from the Engine Module:
- 18057 – 104 Powertrain Data Bus: Missing Message from ABS controller: P1649
- 16885 – 228 Vehicle Speed Sensor: Implausible Signal : P0501 – sporadic 004
I occasionally get the following message from the ABS module:
- 18256 – 035 Please check DTC Memory of Engine Controller : P1848 – Static – No ...

But sometimes in the error state if I try and read codes from the ABS module I just hear the ABS module buzz (from the pump) several times, which I don’t get other times when I read the ABS codes. And then I get the message “LINK FAILURE” like it cant connect to the ABS module.

I have already checked the green connector on the back of the cluster and the green connecter at the base of the passenger A-pillar to make sure they are secure as in understand these both contain vital abs connections, and also checked the connector on the ABS unit.

I really need to work out if the VSS (vehicle speed sensor) is causing the ABS comms issue or if the ABS module is shot and throwing a red herring with the VSS code.

Am I right in saying the VSS on the 2003 b6 s4 is the front left ABS sensor? And that it has no VSS on the transmission?

My gut instinct is that the ABS control module has had its day. Which is fine I am able to detach the control module from the abs unit without loosing the brakes. And send it for repair fairly easily and cheaply (about £80).

But i just want to make sure that it’s not more likely to be the ABS sensor before i send the ABS module off, or I dread to think it may be some CAN bus wiring (god I hope not!)
Can anyone help on this or know someone that can help?

[TimE-J]

As far as I can tell the vehicle speed is found using the N/S/F wheel speed sensor.

I have changed a couple of ABS modules on B6 and B7's so could well be the problem. Im my experience CAN-BUS wiring rarely goes wrong unless its been physically damaged and chaffed.

[Monkeymagic]

Do a full scan first bud

[re2500]

As far as I can tell the vehicle speed is found using the N/S/F wheel speed sensor.

I have changed a couple of ABS modules on B6 and B7's so could well be the problem. Im my experience CAN-BUS wiring rarely goes wrong unless its been physically damaged and chaffed.

Hi Tim,
Thanks for your input
All the wiring is in good condition throughout the car, even the areas that are known to get damp in the b6/b7 are dry and a little dusty. The only modifications that are wiring related is the LPG system but this seems to be a stand alone system.
I think i may just bite the bullet and send my control module off to these guys for diagnostics and repair:

http://autotekelectronics.com/autotek/?Page=PopupPart&PartID=1479

They have a "repair mine" option which looks good value and avoids any coding issues when refitting.

Do a full scan first bud

I would do mate, but my hand-held code reader won't do a full scan. I can only retrieve codes from individual modules. Which is better than nothing i suppose.

[TimE-J]

Your not popping up this end anytime soon are you? or if you can hold on till ADI time I could bring down my diagnostic gear Delphi/Vag-Com.

[re2500]

Nah, im afraid not and you're a bit of a drive from me. Thats a good offer mate, thanks, but i really want to get it sorted ASAP really.
Driving around with flashing warning lights and no speedo, as well as no cruise control is annoying.
Oh, another weird symptom of the fault is a change in throttle response, it seems in the fault state if i stay in gear and very gently go from acceleration to deceleration on the throttle, i get a bit of driveline shunt. like its just shutting of the throttle digitally.

[re2500]

Ive decided not to use autotek, any mention of them on the net seems to be bad. Ill now send the unit to ACtronics theys seem to get good reviews and its unlikely to cost more than £100 including return postage, which includes 24months warranty.

[Monkeymagic]

Have you tried watching the signals from each wheel speed sensor on VCDS?. I suspect the culprit is the VSS.

[Error404]

AFAIK the VSS is taken from the front left ABS sensor. Without knowing much about the controllers etc I'd be inclined to think the sensor was bad or the ring was dirty / cracked or got something metallic jammed in it. The inner tripoid CVs have quite a range of plunge on them, if you remove the hub bolt you might be able to pull enough of the outer CV out of the upright/hub to have a look without removing any of the ball joints

[re2500]

As i mentioned earlier i dont have vcds or vagcom, only a handheld reader.
Ok cool, i'll get ti in the air and spend some time checking out the vss on saturdqy before sending off the control module. I'll check for anything obvious about the sensor or the signal ring. Other than that i can swap the sensors left to right on the front and see if the codes change.