2009 W164 ML350 Wheel speed sensor issue

[DuncanML350]

Hi all

I have a problem with my 2009 W164 ML350.

I have warning lights indicating ABS fault i have plugged into diagnostics and found that it is showing a wheel speed sensor fault tested all the sensors and they are ok, so now i am looking at the magnetic ring on the hub/bearing or wherever it is.

One of them is showing signs of wear when you look down the hole that the speed sensor fits into, is this a common fault?

If so can i just buy the sensor ring on it's own or do i need to buy a complete wheel bearing as i have been told?

Any help appreciated.

 

[Bellow]

If your set-up is as per most others, the ring isn't magnetic but soft iron which when exposed to the elements is corrosion prone but not wear prone as nothing contacts it. Nor can it indicate via diagnostics when stationary - only its effects when in motion which may or may not be logged.

If your diagnosis is showing a hard fault (but sensors OK as you say) possibly the wiring to them is damaged.
If your diagnosis is showing a logged fault of misreading, then the ring is a suspect but other factors can give rise to erroneous signals which will trigger ABS (eg tyre mismatch) but wont generally illuminate the dash light permanently.

 

[DuncanML350]

Thanks for the reply.

Ok so maybe it is just a bit corroded, will have another look

That is a good point on the diagnostics not registering the fault when stationary.

I will have another look at all parts at the weekend and get some diagnostics on it again.

Thanks

 

[DuncanML350]

One thing in addition if i do need to replace this ring is it something i can buy on it's own or is it part of a full wheel bearing unit?

 

[Bellow]

One thing in addition if i do need to replace this ring is it something i can buy on it's own or is it part of a full wheel bearing unit?

Don't know - some MB cars have them embedded in the bearing but I don't know which ones. If embedded, it should be corrosion proof (I'd have thought) if external more likely to suffer corrosion (they weaken and split and the gap across the split causes a misreading) but easier replaced.
Google search 'front ABS reluctor ring for (insert car and age of it here)' and see what comes up. Or, same for a wheel bearing and see if there is a mounting point for an ABS sensor.
Or wait for a ML350 owner to appear and advise!

Permanently lit dash light suggests wiring fault though.

 

[DuncanML350]

Ok thanks - still searching some say it is built into the wheel bearing and some say you can buy the ring separately but i can't find a listing for it. Will do some phoning around thanks for your help