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Re: Re: ABS activating at <5mph
Not sure who started the discussion about intermittent ABS
operation; I first took notice of it in digest number 2127, in
a post from Kirby Smith quoting Fred Munro, Sherry and
Chuck Clark, and Chad. But I figure I'll throw out my
recent 90Q ABS experience for consumption. Hopefully,
it will help someone else save some money.
My ABS would occasionally deactivate itself at low speeds.
I could press the ABS switch twice to reactivate, and
everything was fine. Then one day, ABS turned itself
off and it would not stay on again. I could double-press
the ABS switch and the ABS-off light would go out, but
about 25 seconds later, it was back on.
I checked out the signal coming from each wheel sensor,
but didn't use an oscilloscope; I used a multimeter. When
placed across the two leads of a functioning wheel speed
sensor, I read approximately plus and minus 100 millivolts
when spinning the wheel under test by hand. I located the
bad sensor this way because I got no signal (well, OK,
I read +- 4mV, virtually nothing). I pulled the sensor out
of the car -- that was pretty easy -- and called an Audi
dealer. With a quotation of $303 for a new sensor, I was
back out in the driveway with a new-found interest in
reviving the dead sensor.
It turns out that the problem was simply a break in the
internal wiring. I had changed shocks about four months
prior and, in so doing, had broken a little white plastic clip
that pressed on one of the strut mounting bolts (actually,
on the nut side). This inexpensive little clip held the ABS
wheel speed sensor lead, and the break in the wiring was
approximately where this clip had been. I guess vibration
of the lead had caused the break, but the wire ends still
touched for a while, hence the intermittency.
I cut open the outer insulation, found and soldered the
break, and put the sensor back. Problem gone.
I love a story with a happy ending, especially when it's
me that's the happy one!