ABS cutting in at low speeds

mryesno · 13th May 2016, 00:39

Hi,

ABS cuts in under very gentle braking, especially at low speeds. I can feel it through the brake pedal. ABS light occasionally comes on. I visually inspected all the ABS speed sensors and checked their resistance with a multimeter. All seemed fine. The speedo works normally.

I took the car to the garage, and they replaced near-side rear speed sensor and bearing. £150 parts, £50 labour. After shelling out about £200 the symptoms were exactly the same, and the ABS light came on on my way home from the garage.

So what could be causing the problem?

And should I expect to get some kind of refund for the £200 I spent which didn't seem to have any effect on the problem?

I've spent about £1500 on a new clutch, brakes and coil springs in the last 6 months, despite the car only being worth about £300, since it's a CAT C write-off. But it's mechanically very sound, and a really lovely car.

Oh, and it's due for its MOT next week. ABS light=MOT failure. The mechanic said he'd try to resolve the ABS problem on the same day it goes in for its MOT. He seems a very reasonable chap, and said that he totally gets that I'm not happy to have paid £200 and the problem's not fixed.

What to do?

FrenchMike · 13th May 2016, 07:32

Hi,stop wasting time and money ,you have to pin point the faulty sensor
(and associated bearing)
proceed like this:

Good luck (hundred threads about it)

Mike

Sector-9 · 13th May 2016, 07:36

Unless they've retrieved live data from the ABS ECU then how do they know they've replaced the correct sensor/bearing? Sounds like they're letting you pay for their guesswork. Firstly, if the light only comes on once moving then the sensors and ECU are (electrically) okay and unlikely to be the fault. Secondly, if your speedo and cruise control still work then you can forget the front sensors. The most common non-electical problems are failure of the magnetic ring on the rear bearings or interference with the rear sensors from flakes of rust. There are loads of recent posts about ABS faults with lots of good advice and test procedures so search out some of those

lesron · 13th May 2016, 19:48

I have a similar problem no abs lights are on brakes fine at high speed , but at low speed coming up to a junction etc gently apply brakes and you feel and hear the pulsing and drop in pressure on the pedel. I hate it so much i just take the abs fuse out and replace it on wet days
Can it really be rust on the magnetic rings or is it the abs control thats at fault

Arctic · 17th May 2016, 08:16

Quote:

Originally Posted by lesron

I have a similar problem no abs lights are on brakes fine at high speed , but at low speed coming up to a junction etc gently apply brakes and you feel and hear the pulsing and drop in pressure on the pedel. I hate it so much i just take the abs fuse out and replace it on wet days
Can it really be rust on the magnetic rings or is it the abs control thats at fault

Hi Les.
Yes rust on the ring will show up the fault, I found this to be the case with mine not long back, I keep meaning to get round to the how to I did but real life gets in the way.

I also found the back plate to be in a corroded condition and as I did not have ant to hand at the time I cleaned the area changed the sensor and the hub, job done I still need to change the back plate when I have time now that I have sourced them, because I am sure if you do not change the corroded back plates the problem will raise it's ugly head once again in the near future

HarryM1BYT · 17th May 2016, 08:50

Quote:

Originally Posted by Sector-9

Secondly, if your speedo and cruise control still work then you can forget the front sensors.

I agree with the rest of your post, but the above part is not correct....

It is possible for those two to work at reasonable speeds, yet for the sensor's output to fail at lower speeds. T4 will define which corner has a problem, as will Frenchmike's multimeter test method and my own adaptation of Frenchmike's method - listening to clicks on a piezo earphone.

His problem is irregular / unreliable pulse output at low speed. Usually that traces back to a sensor being slightly too far away from the disk. So his first problem is to determine which sensor is misbehaving, then file the lug to allow it to go in to its socket deeper.

His garage should fix the issue for what he has already paid, but many garages know little of the techniques of testing ABS.

The sensor should not only produce those voltages, but produce the voltage changes with absolute regularity. The only way to prove that is to mark the tyre wall with chalk, at every pulse and roll the wheel round a few times, to make certain the pulses always show up at the marked points.

ABS is triggered by a pulse(s) failing to appear, when compared to the output of the other wheels.

Mike Noc · 17th May 2016, 18:26

Yes I found exactly what you have mentioned Harry. When one of my rear sensors was playing up I connected a home made extension lead and plugged it into the OSF ABS plug.

The speedometer worked perfectly - the sensor was only missing the odd segment at very slow revolutions of the wheel, when the speedometer would hardly be registering anything anyway.

In my case it was a slightly too big air gap between sensor and the magnetic reluctor in the bearing - both aftermarket items. Easily found using French Mike's voltage test.

sewerman · 13th May 2016, 21:49

Had exactly the same problem a t4 session soon found which wheel and just changed the bearing problem sorted. How did the garage know which side to change ?

Sent from my SM-T530 using Tapatalk

mryesno · 14th May 2016, 00:24

I'm going to o try FrenchMike's suggestion tomorrow, with the help of this more detailed guide... http://www.macfadyen998.plus.com

My suspicion is that they simply fitted a new sensor and bearing to the wrong wheel. I don't know how they selected the wheel they did. Would an average independent garage have the diagnostic systems to read a fault code from the abs system? There are no faults in the main ECU according to my cheap bluetooth obd2 adaptor and phone app.

If I get my multimeter out and find an obvious fault with the sensor or bearing on a wheel other than the one they fixed, then it will be obvious that they 'fixed' the wrong wheel... won't it?

If that's what I find, can I explain to the garage that they erroneously replaced the sensor and bearing for the WRONG WHEEL, and they'll give me a refund? Or will they claim that both hubs/sensors co-incidentally stopped working simultaneously?

Anyway, thanks for the advice, everybody!

mryesno · 14th May 2016, 00:36

Another thing... The speedo works normally, so I think I can rule out the front right sensor/hub.

When I use the diagnostic mode, activated via the trip reset button... http://www.the75andztclub.co.uk/foru...ad.php?t=55585... I get 2 similar speeds indicated (via 7.3 and 7.4). Which wheel speed sensors do these figures refer to? Front left and front right? If so, since the mechanic replaced he sensor and hub on the rear left wheel, that leaves the rear right sensor/hub as the one to test with my multimeter. Is that right?

13th May 2016, 00:39	#1
mryesno Newbie Rover 75 CDT 2002 Join Date: Nov 2014 Location: Totnes Posts: 12 Thanks: 0 Thanked 0 Times in 0 Posts	ABS cutting in at low speeds Hi, ABS cuts in under very gentle braking, especially at low speeds. I can feel it through the brake pedal. ABS light occasionally comes on. I visually inspected all the ABS speed sensors and checked their resistance with a multimeter. All seemed fine. The speedo works normally. I took the car to the garage, and they replaced near-side rear speed sensor and bearing. £150 parts, £50 labour. After shelling out about £200 the symptoms were exactly the same, and the ABS light came on on my way home from the garage. So what could be causing the problem? And should I expect to get some kind of refund for the £200 I spent which didn't seem to have any effect on the problem? I've spent about £1500 on a new clutch, brakes and coil springs in the last 6 months, despite the car only being worth about £300, since it's a CAT C write-off. But it's mechanically very sound, and a really lovely car. Oh, and it's due for its MOT next week. ABS light=MOT failure. The mechanic said he'd try to resolve the ABS problem on the same day it goes in for its MOT. He seems a very reasonable chap, and said that he totally gets that I'm not happy to have paid £200 and the problem's not fixed. What to do?

13th May 2016, 07:36	#3
Sector-9 Gets stuck in Rover 75 CDT manual Tourer Join Date: Aug 2014 Location: nr. Mansfield Posts: 767 Thanks: 24 Thanked 182 Times in 137 Posts	Unless they've retrieved live data from the ABS ECU then how do they know they've replaced the correct sensor/bearing? Sounds like they're letting you pay for their guesswork. Firstly, if the light only comes on once moving then the sensors and ECU are (electrically) okay and unlikely to be the fault. Secondly, if your speedo and cruise control still work then you can forget the front sensors. The most common non-electical problems are failure of the magnetic ring on the rear bearings or interference with the rear sensors from flakes of rust. There are loads of recent posts about ABS faults with lots of good advice and test procedures so search out some of those __________________ Free fault codes scan/clear (TOAF) - M1 J27 area

13th May 2016, 07:32	#2
FrenchMike This is my second home Rover 75 Saloon Join Date: Aug 2007 Location: Avignon Posts: 4,466 Thanks: 94 Thanked 661 Times in 554 Posts	Hi,stop wasting time and money ,you have to pin point the faulty sensor (and associated bearing) proceed like this: Good luck (hundred threads about it) Mike

13th May 2016, 19:48	#4
lesron Avid contributor rover 75 saloon and tourer Join Date: Jul 2015 Location: Hythe Posts: 162 Thanks: 31 Thanked 9 Times in 9 Posts	I have a similar problem no abs lights are on brakes fine at high speed , but at low speed coming up to a junction etc gently apply brakes and you feel and hear the pulsing and drop in pressure on the pedel. I hate it so much i just take the abs fuse out and replace it on wet days Can it really be rust on the magnetic rings or is it the abs control thats at fault

17th May 2016, 18:26	#7
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: 11,552 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Yes I found exactly what you have mentioned Harry. When one of my rear sensors was playing up I connected a home made extension lead and plugged it into the OSF ABS plug. The speedometer worked perfectly - the sensor was only missing the odd segment at very slow revolutions of the wheel, when the speedometer would hardly be registering anything anyway. In my case it was a slightly too big air gap between sensor and the magnetic reluctor in the bearing - both aftermarket items. Easily found using French Mike's voltage test.

13th May 2016, 21:49	#8
sewerman Gets stuck in MG ZT+ CDTi Join Date: Feb 2014 Location: Wolverhampton Posts: 632 Thanks: 166 Thanked 264 Times in 154 Posts	Had exactly the same problem a t4 session soon found which wheel and just changed the bearing problem sorted. How did the garage know which side to change ? Sent from my SM-T530 using Tapatalk

14th May 2016, 00:24	#9
mryesno Newbie Rover 75 CDT 2002 Join Date: Nov 2014 Location: Totnes Posts: 12 Thanks: 0 Thanked 0 Times in 0 Posts	I'm going to o try FrenchMike's suggestion tomorrow, with the help of this more detailed guide... http://www.macfadyen998.plus.com My suspicion is that they simply fitted a new sensor and bearing to the wrong wheel. I don't know how they selected the wheel they did. Would an average independent garage have the diagnostic systems to read a fault code from the abs system? There are no faults in the main ECU according to my cheap bluetooth obd2 adaptor and phone app. If I get my multimeter out and find an obvious fault with the sensor or bearing on a wheel other than the one they fixed, then it will be obvious that they 'fixed' the wrong wheel... won't it? If that's what I find, can I explain to the garage that they erroneously replaced the sensor and bearing for the WRONG WHEEL, and they'll give me a refund? Or will they claim that both hubs/sensors co-incidentally stopped working simultaneously? Anyway, thanks for the advice, everybody!

14th May 2016, 00:36	#10
mryesno Newbie Rover 75 CDT 2002 Join Date: Nov 2014 Location: Totnes Posts: 12 Thanks: 0 Thanked 0 Times in 0 Posts	Another thing... The speedo works normally, so I think I can rule out the front right sensor/hub. When I use the diagnostic mode, activated via the trip reset button... http://www.the75andztclub.co.uk/foru...ad.php?t=55585... I get 2 similar speeds indicated (via 7.3 and 7.4). Which wheel speed sensors do these figures refer to? Front left and front right? If so, since the mechanic replaced he sensor and hub on the rear left wheel, that leaves the rear right sensor/hub as the one to test with my multimeter. Is that right?