ABS off at 120-130 km/h (75-80 m/h) 87 5kq - update & redux

[Fred Munro]

Hi Geo;

I've never had this problem, but I suspect the reluctors on the CV joints.
They tend to get rust and assorted crap packed in between the splines and
this reduces the signal strength. The splines also corrode away with the
same effect. It sounds like the ABS computer is losing the signal from one
or more sensors at 130 kph and shutting off the system.
Try cleaning the CVJ reluctors and inspecting them for wear. Not an outside
job on a cold and snowy day!

HTH

Fred Munro
'94 S4  123k km

----- Original Message -----
From: "GEORGE MILLS" <gamills at ns.sympatico.ca>
To: <quattro at audifans.com>
Sent: Tuesday, February 13, 2001 2:30 PM
Subject: ABS off at 120-130 km/h (75-80 m/h) 87 5kq - update & redux


> Hello you crazy bunch! I see cabin fever is high, must be all the
> snow. I didn't get any hints for a possible fix on this so I did a few
> prelimary checks as per BM. Everything checks out at the power supply
> relay for anti-lock. I don't have the $$$$$ Bosch anti-lock system
> tester, so I just used my trusty available equipment. We have a light
> snow coming down here today, and it's not too friggin' warm either.
> However, the car was warm and I just set the heat to high. I was half
> in/half out of car playing contortionist trying to get at the power
> supply relay, pulled it and got these results:
> *I checked the usual, fuse, anti-lock switch on, connections good on
> modulator, no fluid leaks apparent, brakes okay, diffs locks off, fuse
> in relay okay.
> *After removing power supply relay, ignition on, I got ~12V between 2
> and 4, 5 and 4. I got ~12V between 8 and 4 with anti-lock switch held.
> With diffs locked I got zeroV and with unlocked got ~12V unlocked.
>
> After this the going gets rough. I would really appreciate it if
> someone who's BTDT or has any reasonable ideas would drop me a line.
> I'm leaning toward crudded up sensor rotors at this point because I
> can't see why the ABS goes off at over 120 km/h. I checked to see if
> the ABS was actually off rather than just the light coming on by
> comin' onto the brakes at the time and I got screeching rubber. If
> it's the sensor rotors I'll forget about it for now.
>
> Thanks for reading and for any input.
>
> Geo
>
> >Anyone have this happen? It's consistent on my luxury German automobile.
If I slow down I can cycle the ABS on/off switch to get it working again,
but I would rather not slow down and have it working. Is it possibly related
to crudded up speed sensor rotors on CVJ? I reset the speed sensors a couple
years ago to try and cure another problem I had with the system that turned
out to be a pump relay in the modulator. I pretty much cleaned everything up
at that time, but not the sensor rotors. I do get occasional ABS activation
when almost at a stop on dry pavement.