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?

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

http://rovermg1.free.fr/rovermg/thum...q0kPm0Jmhg.jpg

Good luck (hundred threads about it)

Mike

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

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

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

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!

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?

Never had the abs light on but as i stated had the pulsing, not know though,striped down the rear drivers hub only to find the back plate rusting away , big clear out of all the rust and checked passenger side not so bad , as i say problem sorted

OK. So today I tested all 4 abs sensors using the above method. Three of the wheels gave readings that oscillated between 0.7 and 1.7 volts as I rotated the relevent wheel - normal. Remember, the garage replaced the NEARSIDE rear sensor. But I found that the OFFSIDE rear sensor was giving me a higher-than-normal voltage - it oscillated between 1.2 and 2.4 volts.

This would seem to be consistent with the symptoms I've been having: the sensor is feeding the abs unit a voltage that oscilates between bit below 1.7v and a bit higher than 1.7v, confusing it into thinking that the offside rear wheel has locked up.

So I'm thinking that the garage must have just replaced the wrong sensor and bearing.

The question is whether they'll refund the £200 I paid. Perhaps they'll tell me that the nearside sensor and bearing were faulty as well. But the symptoms only appeared a couple of days before I took it to the garage and their repairs had no effect on the symptoms. So that would seem to much of a coincidence to be plausable.

Anyway, thanks again for all your advice, people!

You've paid them to fix a fault and they haven't (the bill isn't just labour for the investigation, it includes parts that likely weren't needed as the chance of two side failing at the same time are remote). Hopefully you paid by credit card in which case get them involved, but even if you used a debit card, provided it was Visa you may be able to do a chargeback. I'd speak to CAB before doing that though.