ABS wheel sensors?

[sproutdreamer]

ABS light comes on sometimes and then goes off. Mostly it is off. MOT coming up and if I am unlucky the light will come on and so will a MOT fail. Car is a 1.3 04 T Spirit and only done 44K miles but still do not want to throw money at it. My first thought was to have a look at the ABS sensors, dirt etc but disappointed to see that the rear ones are pressed into the hub-what poor design to have to replace the hub if there is a faulty rear wheel sensor.

Anyway I am probably rushing into assumptions. Any advice as to best go about diagnosing what is happening. I have run diagnostics and there are no fault codes left showing.

[Madasafish]

You need a full fault reader to get ABS diagnostics. A cheap one only reads engine faults.

You might  need a multimeter  but hopefully not.

The most likely failing is the front passenger ABS. Either the wiring is failing or the sensor is.. but an intermittent fault is usually caused by corrosion of the rotating teeth mounted on the drive shaft. The sensor picks up the rotation and the ABS ECU measures speed. IF there is corrosion or dirt on the sensor - or more likely the teeth, you may get an intermittent fault. So jack up car, remove wheel, undo sensor retaining bolt and inspect sensor - and look at ring through hole and rotate hub to check all round. WARNING: sensor wiring is sensitive and prone to damage . Handle with great care.  

Chek both front hubs. But one at a time and then test each side by driving before starting on the other.

You can only check the fronts like that. The rears require testing of voltages and resistances on the rear hubs = which means disconnecting the wire feed and testing the resistance from each wire . Ignition off. You will only get a problem if resistance is zero - faulty sensor - short or infinite -broken wire. The only time you can test is when the ABS warning light is illuminated so the fault is present. But the likelihood is a front fault passenger side as exposed to more salt and crud.

[sproutdreamer]

Thanks  Mad...

I was just checking whether my freeware diagnostics did ABS codes and even the paid version does not mention ABS so I will get a better/paid for OBD11 diagnostics software. There are lots out there have you a recommendation?  I will check out the front sensors when I have run a proper diagnostic check.

[Madasafish]

The all singing all dancing ones are something I have never taken an interest in. Car Mechanics does regular tests..

[sproutdreamer]

I sheared the bolt taking out the passenger side front one. The sensor was covered with rust flakes from the rusty hub hole it sat in. I sheared the bolt and had to drill and retap the thread as it was rusted solid. I still have the other side to check ...or not! I think I will wait to see if I have fixed it.

[Mick F]

Our Clio needed new drive shafts due to the rust on the serrations on the outer surface.  The sensors were ok.  Nowt wrong with the drive shafts themselves, just the rusty serrations and bits had broken off them.

£166 for the pair (fitted by our local independent) in April 2010.

Mick.

 

[sproutdreamer]

Thanks to Madasafish - the passenger side sensor WAS choked with rust flakes stuck to the sensor magnet and the toothed wheel was also very dirty with rust and other debris. cleaned it all up and bingo all is good with ABS. Including snapping the securing bolt and drilling it out and retapping the thread it took me about 2 hours.

[sproutdreamer]

Not completely all good. Cleaned out the driver side front sensor, also having to drill out and retap the another broken screw. Again clustered with iron scale to the magnetic sensor. All seemed ok but ABS light came on again on my way to the MOT test! Happily it did not come on during the test but the car failed due to siezed rear drum cylinders giving unequal braking and difficulty balancing handbrake cable play and binding brakes. It may be that the siezed cylinders were a little out causing problems getting the brakes handbrale lever set up properly.

Strangely all the cheapish ABS sensors online seem to be the passenger side? Are these sensors handed or coded as RH or LH apart from the little bracket that hooks behind the bolt attaching the brake flexible hose to the suspension leg. It would help if I just got 2 LH sensors and swapped over the old bracket for the driver side?

[sproutdreamer]

Bought a LH front wheel sensor new only £9.04 from atp-spareparts. It arrived in 3 days from Germany! So if the light comes on again I will swap the LH sensor for the new one and if the light comes on again swap the LH sensor into the front RH wheel. I have a feeling that only the clip on bracket is handed and that the sensors are the same so I will just re-use the old RH bracket, if it comes to that.

Retest MORT on Monday I just hope it behave until Tuesday.

[Madasafish]

Sensors are the same: just brackets differ.

[sproutdreamer]

Thanks madas.. I suspected that. Having cleaned both sensors after retapping screw threads it has settled down with no ABS light coming on, so I have a semsor ready if it starts to act up again.