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Old 9th September 2020, 12:49   #1
Pueblo_Boy
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Default ABS light, speedo not working

I've searched on the forum, but wanted confirmation please...

My ABS light suddenly came on, and the speedo registered zero whilst I was driving along. Mileometer does not work, and the speed on the 'electronic screen' shows as zero also.

Is this a simple ABS sensor problem on the front driver's side? What do I need to replace? Is there any need or recommendation to replace the bearing (given the car has done 155k miles)?

All advice appreciated.
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Old 9th September 2020, 13:00   #2
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Yes it is the front driver's side at fault, but you need to do a bit of further investigation to determine whether it is the ABS sensor, a bit of rust preventing the sensor from detecting the reluctor segments, a wiring fault, or the magnetic reluctor in the wheel bearing.
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Old 9th September 2020, 15:09   #3
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Quote:
Originally Posted by Mike Noc View Post
Yes it is the front driver's side at fault, but you need to do a bit of further investigation to determine whether it is the ABS sensor, a bit of rust preventing the sensor from detecting the reluctor segments, a wiring fault, or the magnetic reluctor in the wheel bearing.
So, it needs to go to the garage? Or could it be a diy job? I might just be able to take the wheel off, but then, I'm lost! Mind you, I do have a Haynes manual somewhere, maybe that can help...
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Old 9th September 2020, 19:32   #4
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Courtesy of French Mike you can check all the ABS sensors and magnetic reluctors in the wheel bearings using a voltmeter.
The signal voltage changes from 1.7V to 0.7V as each magnetic segment passes the sensor, so jack each wheel in turn and slowly rotate it marking the switch points on the tyre wall with chalk. You should end up with 48 chalk marks looking something like this:





If any gaps are in the same place each revolution then likely a damaged reluctor, and if in random places suspect the sensor.
Other common failure causes are cable damage to the sensors, flakes of corrosion interferring with the sensing, or corroded plug pins at the ABS modulator.


You connect the positive probe of the multimeter to the signal wire, and the negative to chassis earth:






I made up a cable from some old bell wire and a scrap ABS plug and socket to save pinning through the cable insulation. Here it is testing a hub prior to fitting:






Last edited by Mike Noc; 9th September 2020 at 19:36..
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Old 9th September 2020, 21:57   #5
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All useful info, thanks.

Funnily enough, off I went to the supermarket today, and everything worked fine...go figure! It's bad enough having a fault, I would say an intermittent one is even worse!
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Old 11th September 2020, 18:58   #6
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Something similar happened to me a couple of years ago on route to Italy. Perfect all the way to Dover for our overnight stop . The next morning on route to the ferry the abs light came on and the cruise control stopped working ( nsf sensor ) which was just what you need on the autoroute! It was intermittent all the way there but fine coming back and has never been on since or been checked! I just think she was feeling a bit nervous as it had been a while since we had toured Europe lol !

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Old 12th September 2020, 11:01   #7
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Smile Partially a DIY job

Quote:
Originally Posted by Pueblo_Boy View Post
I might just be able to take the wheel off, but then, I'm lost!
  1. Take off road wheel.
  2. Identify two electric cables running vertically upwards behind the road spring.
  3. Trace them back to the wheel hub. One leads to the brake pads. You don't want that one.
  4. The other leads to the ABS sensor. Inspect this cable closely. Has it popped out of its clip on the suspension strut?
  5. More to the point, has the cable insulation been worn away (by the tyre at, or near, full lock)?
  6. If so, all you need is a new sensor. They're not expensive, but getting the old one out may be a job for your garage.

Good luck!

Simon
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