Following the deathly silence on my request for info, I've finally sorted it 
out and discovered some gen which you may find useful.
Most abs sensors are exposed to the elements. The fronts are subjected to 
all the crap the road can throw up plus gunge deposited from the front 
brakes. Since asbestos was banned brake pads have a helluva lot of metal in 
them. Discs wear out  70% faster with modern pads. A lot of that metallic 
powder is thrown over the rotator segments on the drive shaft and the tip of 
the abs sensor mounted adjacent. The abs sensor sends signals to the ecu as 
a magnetic induction sine wave.
Cover the sensor in metallic powder(magnetic) and the abs ecu will detect a 
supposed fault. On goes the warning light on the dash and no MoT until its 
fixed.
Whenever you have a wheel off, it's worthwhile cleaning up the sensor and 
rotator whilst it's accessible. Old toothbrush and contact cleaner is 
useful.
BTW-Citroen Xantia abs sensor 50 from main dealer. (Old one probably ok 
with a clean up).
Here endeth the lesson.
DaveK.

"davek"  wrote in message 
news:dfi41h$v6f$1@news6.svr.pol.co.uk...

> Following the deathly silence on my request for info, I've finally sorted 
> it out and discovered some gen which you may find useful.
> Most abs sensors are exposed to the elements. The fronts are subjected to 
> all the crap the road can throw up plus gunge deposited from the front 
> brakes. Since asbestos was banned brake pads have a helluva lot of metal 
> in them. Discs wear out  70% faster with modern pads. A lot of that 
> metallic powder is thrown over the rotator segments on the drive shaft and 
> the tip of the abs sensor mounted adjacent. The abs sensor sends signals 
> to the ecu as a magnetic induction sine wave.
> Cover the sensor in metallic powder(magnetic) and the abs ecu will detect 
> a supposed fault. On goes the warning light on the dash and no MoT until 
> its fixed.
> Whenever you have a wheel off, it's worthwhile cleaning up the sensor and 
> rotator whilst it's accessible. Old toothbrush and contact cleaner is 
> useful.
> BTW-Citroen Xantia abs sensor 50 from main dealer. (Old one probably ok 
> with a clean up).


Similar problem with my Fiat Bravo - only I went over a speed bump a bit 
quick, must have knocked the crud off the sensor cos it works like a charm 
now!

Hellraiser..........>

"davek"  wrote in message
news:dfi41h$v6f$1@news6.svr.pol.co.uk...

> Following the deathly silence on my request for info, I've finally sorted
it
> out and discovered some gen which you may find useful.
> Most abs sensors are exposed to the elements. The fronts are subjected to
> all the crap the road can throw up plus gunge deposited from the front
> brakes. Since asbestos was banned brake pads have a helluva lot of metal
in
> them. Discs wear out  70% faster with modern pads. A lot of that metallic
> powder is thrown over the rotator segments on the drive shaft and the tip
of
> the abs sensor mounted adjacent. The abs sensor sends signals to the ecu
as
> a magnetic induction sine wave.
> Cover the sensor in metallic powder(magnetic) and the abs ecu will detect
a
> supposed fault. On goes the warning light on the dash and no MoT until its
> fixed.


I gave the same information about metallic dust on sensors, in a reply to
Hellraiser about a fortnight ago, in the thread 'Fiat Bravo ABS failure-what
to check'
Your earlier enquiry asked for details of how to remove the sensor on a
Xantia, about which I didn't have a clue.
Mike.

> I gave the same information about metallic dust on sensors, in a reply to
> Hellraiser about a fortnight ago, in the thread 'Fiat Bravo ABS 
> failure-what
> to check'
> Your earlier enquiry asked for details of how to remove the sensor on a
> Xantia, about which I didn't have a clue.
> Mike.


Right, missed that earlier thread.
DaveK.