ABS sensor problem continues
 

Still chasing a mysterious rear sensor issue. Sensor passes the static test, but warning light comes on when driven. Pscan identifies a signal error right hand rear.
So far I have had three different hubs firtted, two of them new. I am about to do the meter test to check the hub and sensor combination.
However, my question is -

Does the ABS ECU compare the speeds of the rear wheels against the front wheels? If not, then if the rear cables connected to two sensors that were NOT fitted to the backplates (and therefore not registering a wheel speed) then the system would pass the static and moving test.
Not ideal of course and it would be a temporary set up so I can mot and tax the car otherwise I'll be without transport.

No it doesn't, well not to start with anyway. I went for a virtual drive once with the front wheels off the ground, and no ABS alarm flagged up. I wasn't driving for long though, and the ABS may well come on after a set time/mileage, so a quick reset before you get to the testing station should get you through.

Thanks for that. The only problem being that my laptop with the pscan on will not hold battery charge so I'd have no way of resetting it when I got to the garage.
However, I'll be checking the sensors both sides tomorrow and the hubs using the meter method and if still no joy will, assuming I still have two new spare sensors, connect them and have an extended test drive.

I'm suprised this issue has not surfaced before as it would be relatively common to have sligfhtly different size tyres front to back which would result in the ASB warning triggering, yet no one to my knowledge has reported this.

Probably designed that way. You wouldn't want the ABS light coming on when the car was on the rolling road at the MOT test where it only drives the front or rear wheels at a time.

What happens if you unplug a sensor and then plug it back in? The system should self test and reset itself, but I haven't tried it myself.

You could eliminate hub & sensor by swapping sides on the rear & then see if the fault code changes sides.


I had a similar issue on a R75 CDTi once & I ended up replacing the ABS ECU which cured the problem.

If you connect the rears left to right and right to left does the fault change sides? (You may need to extend cables) if it is the hub and or the sensor then it should. If it doesn't then the fault is upstream.
Totally not recommended as its an absolute bodge but if you splice the cable from the working side into two and fed both rear abs feeds back upto the module would that extinguish the abs light for the MOT?

That's a thought, however I've only enough plugs and sockets to cross connect one sensor, but I will investigate.
I suppose the pscan is reporting the correct that has failed, telling me it's the right side when it could be the left side failed? I'm sure someone would have found this issue by now.

As I've just posted, I don't have enough bits to cross connect both sides at the same time but I wonder if connecting the one known good side to both cables from the ecu would work? - I sort of doubt whether the that set up would pass the static test.
However it that works it may be a bodge but the car's safety would not be impaired as the ABS would still work on the front wheels which is more important than the rears.


Many things to try, the first being connect two sensors but leave them not fitted to the swinging arms (both will record the same zero speed but if the ECU does not compare front and rear wheels then this will work.


Other problem is airbag plug under drivers seat, I keep messing with it but it very quickly loses connection. Posible solution Scotch loc links for both wires?

Hi Mike.
Why not run your car over to Big Russ and get it on the T4 i am sure that would pinpoint the problem for you, are the back plates in decent condition, is the sensor close enough to the bearing.

Hi I recently had an issue similar to this .
And my diagnosis was believe it or not was corrosion between back plate and axle. Replace back plate cleaned stub axle and problem solved . Have a good look at back plate as the corrosion I believe may have put sensor out of spec good luck