ABS sensor problem continues

p2roverman · 23rd August 2020, 13:17

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.

Mike Noc · 23rd August 2020, 15:13

Quote:

Originally Posted by p2roverman

Does the ABS ECU compare the speeds of the rear wheels against the front wheels?

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.

p2roverman · 23rd August 2020, 16:50

Quote:

Originally Posted by Mike Noc

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.

Mike Noc · 23rd August 2020, 17:58

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.

mh007 · 23rd August 2020, 18:17

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.

stocktake · 23rd August 2020, 18:34

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?

p2roverman · 23rd August 2020, 22:59

Quote:

Originally Posted by mh007

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

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.

23rd August 2020, 13:17	#1
p2roverman Gets stuck in Rover 75 Connie Tourer & Connie SE Saloon & Club SE Tourer Join Date: Sep 2014 Location: Leeds Posts: 975 Thanks: 199 Thanked 71 Times in 59 Posts	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.

23rd August 2020, 18:34	#6
stocktake Vis Whiz Rover 75 2.5 auto Saloon Join Date: Jun 2007 Location: LEEDS Posts: 20,591 Thanks: 2,057 Thanked 3,056 Times in 1,621 Posts	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? __________________ Dave... Lost a few stones and a Gall Bladder and part of a bile duct and all of my dignity in the suppository incident

23rd August 2020, 17:58	#4
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,550 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	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.

23rd August 2020, 18:17	#5
mh007 This is my second home MG ZT260 SE, MG ZT190+, MG ZTT 160, R75 Conn SE 2.0, R75 Conn SE 2.5 X 3, R75 Club SE 1.8, P5B Coupe Join Date: Jul 2009 Location: Keynsham, Bristol Posts: 4,211 Thanks: 65 Thanked 635 Times in 499 Posts	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.