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

GEORGE MILLS gamills at ns.sympatico.ca
Tue Feb 13 15:30:52 EST 2001

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.


>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.

More information about the quattro mailing list