Re: Re: ABS activating at <5mph

[Dan Hall <Daniel.R.Hall@digital.com>]

	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!

	-Dan