ABS warning light
 

I have looked at previous threads on this but can't find circumstances similar to mine so I thought I would post a new one as I'm sure there's lots of experience out there.

My ABS warning light came on the other day and at the same time my speedo stopped working and my fuel gauge was not registering correctly. From what I'd researched on here I narrowed it down to my front offside sensor.

The day before I'd driven through some heavy rain and through a number of quite deep puddles in the road. I checked the blue connector under the bonnet as well as the wire going to the front hub and all seemed to be dry and ok. This was not to be unexpected as the front sensors was replaced about 4 months ago at a garage when the wheel bearings were replaced. It was a sunny day when I checked everything and the warning light did not come on so I put it down to getting water in the system and that this had dried out.

The next morning I found that when I started the car the light was on again. I drove if for a mile or two, switched the engine off and restarted and everything was ok once more. Again I put it down to residual dampness probably made worse by the damp morning which got dried out after a couple of miles driving.

This went on in a similar way for a couple more days but now the light is on and won't go off if I restart the car.

Is there something else I should be checking? I'm assuming that the sensor is ok because it is nearly new. I did try to remove it from the hub to check bit it was stuck quite fast and I didn't want to break it while removing it and wasn't really sure that there was much to check once removed.

Any suggestions will be gratefully received.

Hi Pugcrew. I can't speak specifically for the Rover, but on other cars where I have experienced intermittent ABS lights, the most common fault is the reluctor ring (the toothed magnetic ring which the sensor picks up on) being at the limit of the range that the sensor can detect. Any play in the wheel bearing (I know it has just been replaced) can take it out of range, and the light comes on. Jack the wheel up off the ground, grasp it at top and bottom, and try to rock it. Any play detected could be the cause of your problem. Alternatively,muck or corrosion on the ring can also confuse the sensor. The gap between sensor tip and ring should ideally be less than 1mm.

Have you checked the connector in the engine bay? I fitted a sensor bought off eBay and it worked for a while but then the warning light started to come on now and again before staying on. Turned out the connector was not seating properly. I bought one from dmgrs and when I connected it you could hear a nice click as it connected. I have had no issues since then.

Check out the multi-plug to the ABS unit under the battery, particularly if you have had a lot of water lately.

See my catastrophe last year at http://www.the75andztclub.co.uk/foru...t=abs+traction

and at http://www.the75andztclub.co.uk/foru...t=abs+traction.
do a search in the Technical Help forum for ABS Traction that might help.

In the end I managed to obtain a new part-loom with plug and a new ABS unit, Follow all advice on bleeding the system, but I found it can be done without power on, although it helps at the end to have the engine running for that little extra "push"!
__________________

Thanks for the replies.

Over the last week it has gone from intermittent to always on so I guess my theory about water getting in somewhere then drying out may not be right.

I will try the connector as you suggest Clarky before I get too involved with anything more complex. I've had similar problems with the airbag connections under the front seats so I'm hoping it will be something simple as that. As the detector is new I'm pretty confident that it will be ok and I know the wheel bearings are good although I will double check when the weather is better and I get the opportunity.

If all that fails it may be the reluctor ring. Does anyone know how I can get to this to see if its corroded or simply needs cleaning?

Before ripping apart ABS bits, you also said that your fuel gauge was playing up and your speedo had stopped working. Speedo could be ABS related but the fuel gauge? Wouldn't it be worth a trip down the coast to Fareham and see CB750 Chris who has a T4 diagnostic computer rather than guessing?

Regards

If the speedometer is failing when the ABS light comes on then it will be offside front related.

Courtesy of French Mike you can check 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.


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, bits of rust caught between the sensor and reluctor ring or corroded plug pins at the ABS modulator.


Here is a front hub being tested prior to fitting. I use an extension cable made up from some old speaker wire and ABS plug and socket which saves pinning through the ABS cables. It also doubles up to allow any sensor to be plugged in to the OSF so that the speedometer can be used as a diagnostic.

https://i.imgur.com/W0VviKD.jpg?1

Did you see the photos of my plug at [https://www.the75andztclub.co.uk/for...php?t=247845]?
I am not versed in attaching pictures very well but this thread has it all.

Due to the weather I haven't had the chance to follow up on this but today I managed an hour between showers.

I've test the front drivers side sensor at the blue connector just above the wing liner. I found that I wasn't getting any voltage on either wire so I assumed that the problem is further back in the system.

I decided to check the plug at the ABS modulator as I've read that they can be prone to water penetration and corrosion.

I removed the battery and the plastic compartment that the battery sits in. There is large metal bracket below this which I didn't remove as I could see underneath it but couldn't see the modulator. Am I missing something? I'd assumed it was going to be obvious.

Just to clarify my car is a 2013 CDTI.

I didn't think it was worth removing the metal bracket as it would have meant unbolting the fuel pump and something else that is bolted to it and it didn't seem that I would be able to see anything anyway.

Can someone help? It would be great if someone could post a photo showing the modulator in it's position.

Can anyone help by posting a photo?