ABS sensor testing

[Russ Maki]

My experience with Audi ABS is non-existent, but I attended a Mercedes Benz
Club of America clinic on electrical trouble shooting a couple years ago,
and the technician teaching the class addressed the issue of failing ABS
sensors. His theory was that most ABS sensor failures occur in the wire
leads attached to the sensor, which develop metal fatigue as they flex --
particularly on the front axle.

The internal breaks don't always show up, the tech said, unless you
"encourage" them a bit with some flexing and twisting -- stresses similar to
those the wires might undergo as the car operates. His approach is to attach
an ohmmeter to the terminals on the sensor unit and then bend and unbend the
sensor wire up and down the line. If you get an open circuit, obviously,
you've found your break.

Of course you could have dirty rotors as well if you haven't checked those.

As I said, this was a Mercedes seminar but I suspect both systems are Bosch.
If that's not the case with Audi, well...never mind.

Russ Maki
Ixonia, Wis.


> From: Eyvind Spangen <eyvind.spangen at c2i.net>
> To: quattro at audifans.com
> Subject: ABS sensor testing
> Date: Mon, 05 Nov 2001 21:11:01 +0100
>
> How do I test the ABS sensors without the ABS-tester? I've measured
> the resistance, they measure OK, but my ABS keeps switching off after
> about 100 metres of driving, and before it switches off, the pump is
> running. I've narrowed it down to sensors, tried reinstalling with new
> caps, but no luck. I guess it's either dirty rotors or just bad
> sensors. I'm thinking that an old-fashioned analog multimeter might
> work, anybody BTDT?
>
> --
> Regards,
> ES
> '90 200TQ, new winter tires, but non-functional ABS & diff lock..