ABS Senosors - How to measure ?

[darko]

should you be able to measure them for resistance etc ? I am pretty sure one has gone faulty on my S3 - both the ABS and traction control lights are on. If i short out the connector to the abs sensor the traction control light goes out however the sensor itself measures open circuit - any help very much appreciated as i need to get this sorted for the MOT - thanks !

 

[RichA3Turbo]

if you have vag-com, measure wheel speed. go in a straight line and see which is not reporting correctly

 

[darko]

thanks rich, have had someone do that and has narrowed it down to the front left sensor - i have checked the cables, all seems ok. the sensor itself measures open circuit and from what i have read the sensor is a coil with a magnet in proximity so the pins should be either side of the coil and therefore should measure some resistance - just need to double check before i head off and pay £50 for a new sensor..

 

[RichA3Turbo]

swap with another corner...see if the fault moves.

Rich

 

[darko]

yeah i think you are right - any idea how to get it out, have removed the allen bolt but it seems to be very happy where it is !

 

[RichA3Turbo]

Yep they are a pain in the ****!! I'd use a bit of WD40 and try and wriggle it out.... levering will probably snap it so go easy.

Rich

 

[darko]

snapped it lol ! yeah real pain, at least i managed to get all the bits out

 

[colinra]

i think the sensor is basically an inductor which is a bit like a coil. so you should get some resistance over it.

when the wheel spins the inductor/sensor 'sees' tooth-space-tooth-space etc and a wave form is produced.

the ECU interprates this wave form and decides if the wheel is spinning/locked up.

just my 2p.

 

[darko]

picked up a replacement sensor at gsf car parts and it does indeed measure resistance over the pins. fitted the new one and the traction control light went out straight away. the abs light stayed on until i drove the car up to about 5mph and the sensor started to measure wheel speed - the light went out and has stayed out so far, all good. the part was £25 from gsf instead of £56 from audi and appears to be of good quality by the way...

 

[hamski]

I have the same problem, but no vag-com. Is there another way of checking which sensor is faulty??

 

[darko]

i dont know of any way other than measuring each sensor to find out which one has no resistance, failing that if you take it to a vw / audi / skoda garage they will tell you, some charge (audi / vw) some dont (skoda) all use the same kit....

 

[neil.c]

The sensor has a coil in which I would assume would read a fairly low resistance, and a voltage is induced across this coil when the vehicle is moving, multimeter time