Abs Light On

[Steve P]

ABS light came on the other day with a bit of juddering during braking. Wife was driving, I wasn't there so I guessing the juddering was the ABS working?

 

Have done a search on this forum so I have an idea of what to look for. My findings don't fit exactly - hence this post!

 

Checked the resistance of all the sensors. 3 of them are 1.2K ohms , the drivers side front is 1.75K ohms. Anybody know if that would be enough to upset the system? The ABS light comes on with the ign and stays on.

 

Have checked the abs sensor rings (as on the CV joints). They all turn with the wheel - so they are not split. HOWEVER! The drivers front ring has shiney metal showing - I'm guessing that the ring has contacted the ABS sensor. So the question is WHY if the ring is not split? This contact could be related to the high resistance - or just coincidence!

 

Have checked the wheel bearing - that seems ok. So that tends to suggest rust build up under the ring has pushed it out to the point where it contacts the sensor but without splitting the ring. Has anybody seen this.

 

I don't want to start just buying bits and replacing them willy nilly - that's too easy and often means bits get bought / replaced that were unnecessary. However I do want to get this fixed asap.

 

If I buy a new sensor and plug it in - will the ABS light go out without driving the car? I don't want to risk fitting the sensor just yet in case the ring touches it. On the other hand I don't want to go down the path of fitting the new sensor, removing the ring/cleaning the rust/ gluing it back on - or buying a new CV joint to find that the ABS light is still on.

 

Any thoughts please.

 

Thanks

[Mirez]

Bit of a tricky one eh! There is also the possibility of a foreign object getting stuck between sensor/hub and the ring/CV - I had a large peice of branch do that once on a mondeo which caused similar damage.

 

You would typically expect the resistance of an ABS sensor to be between 1K and 1.5KOhm so that one is showing a slight problem but I wouldn't of thought enough to generate a fault condition, how badly worn is the sensor ring?

 

The easiest method of testing the sensor itself is to trick out the one you suspect to be faulty - pop down to Maplins (or the like) and buy a 1K resistor (about 2p lol) disconnect the suspect sensor and hold the resistor in place on the two wire terminals, turning the ignition on should yield no abs light staying on.

[Steve P]

Thanks - i had thought of resistor - wasn't sure if these sensors are just a plain coil or if there is more to them than that - such that a resistor would trick the system.

 

Have ordered a new sensor - only

[Steve P]

Well - I've fixed it - sort of!

 

Bought the new sensor - resistance measured 1.2K ohms just like the three others on the car.

 

Fitted the new one. Spun the disc and there seemed to be clearance between the ring and the sensor - just.

 

Took the car for a spin - ABS light went off at about 20 mph.

 

However there was a loud rubbing noise from the drivers front wheel. Got back home after a short run round the block and sure enough the sensor was contacting the ring. That was obviously why the old sensor had failed - contact with the ring had damaged the end of it and probably let water in causing the coil to fail.

 

Have fixed the problem for the moment by putting a washer under the sensor to hold it further away from the ring. It still picks up movement of the wheel but clearly something is not right. I can't believe that the new sensor is too long. Even though it is a cheaper copy the fact that the old sensor had contacted the ring and failed is too much of a co-incidence. The ring isn't split and looks fine to be honest.

 

I have to think that that the wheel bearing is on it's way letting the wheel and cv move up under the weight of the vehilce and the senor and ring gap to close.

 

The bearing seems alright but a few years back we had the top suspension mounts done and I know that they didn't replace the CV bolt. These are supposed to be use once and then fit new. It wasn't very tight and without the right load holding the bearing together this may have caused th bearing to wear - although the old gal is coming up on 100k now so things are bound to wear.

 

Any thoughts - I think I'll get me a new bearing - on holidays in a few weeks and don't want that to go!!

 

Cheers

Steve

[Steve P]

Update - no further problems - didn't get round to looking at the wheel bearing - been on hols - no more abs lights. Why the old sensor should fail - and it did look as though it had contacted the ABS ring - and the new sensor contacted the ring I don't know. Perhaps there is corrosion on the CV joint under the ring forcing it outwards a bit? If so the ring will probably be the next bit to break - can't wait!!

 

Cheers

Steve