VW ABS sensor resistance/voltage

[DIYspanner]

Bora TDI

What's the typical valves to expect measuring the resistance and then the voltage when the ring is spun?

 

[Burnerman]

I have tested these with an oscilloscope......I'm not sure of the exact values but here goes (Mercedes Sprinter van, 60 plate)
The sensor at rest had a resistance of around 1.7kOhms. This must be constant. One sensor out of the four had a resistance that climbed on its own accord - I've no idea why though.
With the wheel revolving I noticed that the voltage generated by the ABS system rose sharply the faster the wheel span. Unfortunately I didn't notice how high the voltage rose. Obviously the oscilloscope was feeding the ABS sensor with a voltage to start with - again I don't know that voltage either.
I did notice that the trace generated was completely smooth though, therefore showing that the reluctor ring was complete and undamaged.
Not much help I'm afraid, but I could identify the dud sensor and replace it - and the ABS light went out.
John

 

[DIYspanner]

Thanks John!

Will be investigating it on Friday. I have the n/s to compare which I'm presuming is still healthy. The bother was the bit of metal that got in to the o/s and slightly bent the ring. The gap I understand has to 1mm so will work to that to straighten it as needed.

The likes of Apec, TRW and Febi, reputable brake brands, make the sensors.

The sensor is an easy replacement. The ring means a new hub, bearing and new set of bolts again just after I've done the struts - the joy!

 

[Burnerman]

You mentioned that the ABS was deploying under normal braking? Now that's a completely new one on me but I guess the distorted reluctor is the reason.....I've never had to straighten one but have replaced a few that had rusted off the driveshaft.
John

 

[Stivino]

The ring means a new hub

Is it not possible to get a new reluctor?

 

[DIYspanner]

ABS is only deploying when the car is just about stopped.

Is it not possible to get a new reluctor?

Yes, a new ring is available but that's what I dread having to do, the work involved.

 

[Stivino]

I've had ABS deploying under normal braking, it was a 2001 Primera with a split reluctor. Because of the location of the reluctor and the fact that there was a bit of corrosion, it was very
difficult to see until the hub was pulled of the shaft. I can't believe that I still have the picture after 12 years.

 

[DIYspanner]

Same here Stivino with a Rover 45TD. Early on when I got the car, the ABS was deploying all the time. First port of call was to an auto sparky for a system check but all was clear. He said it must be the rings. I looked, saw both the front were split, got new ones, fitted them and all was well.

Sadly, if the Bora's ring needs replacing, the wheel hub has to be removed and that won't come out without dragging the inner race of the wheel bearing with it.

 

[Mottie]

I had all sorts of ABS problems on a Mondeo once when I fitted a pattern part front wheel bearing with built in ABS reluctor. Tried another, same problem. Fitted a genuine OE bearing, all ok.