ABS wheel sensor fault after sensor replacement.

geoffus · Oct 29, 2021

Came back from holiday in the Lake District and 20 miles from home EML came on and display says "ABS fault", "runflat indicator inoperative" plus other faults even "reverse not available".
Everything pointed to ABS wheel sensor failing, the car was left for a few minutes then restarted and worked fine, few miles down the road the fault returned, this carried on several times and has done so since.
Today I replaced the left front sensor with a Febi Bilstien part, changing it was straight forward but on a road test I have the exactly. same problem, if anything its worse.

So I put the Icarsoft on and reset all the codes, then monitored the wheel speeds on a short run, its fine until I get to around 25mph and the fault re-appears.
Below this speed it drives OK, soon as I go faster the EML light is on and all the faults return.

Anyone had this problem ?
Could it be reluctor ring corroded and not helping to produce a strong signal ?
Why when I then reduce speed the Icarsoft still shows no road speed for the Left front wheel ?
After codes are reset the left wheel shows its now turning again until it reaches 25mph, does the ECU turn the speed monitor off ?

Looking at a series of photos taken on a short drive, it seems the left front wheel spreed drops off while the other wheels increase.
I wonder if the ABS will not operate until the car reaches 25mph and at that point it sees a imbalance in wheel speeds and shuts down.
The car is a 2012 B200 W246 model,

Jobsworth · Oct 29, 2021

Now, don’t take this the wrong way, but I’ve seen aftermarket scan tools get left and right muddled on mercedes cars before. Just to confirm that you are on the right track I would swap the sensors left with right. Just to be sure you aren’t barking up the wrong tree

KennyN · Oct 29, 2021

Had a kind of similar issue with the boys Clio a while back , long story short it was a split in the reluctor ring that only caused an issue at speed when the centrifugal force on the driveshaft allowed the gap to increase slightly causing a blip in the monitoring system leading to an ABS fault.

It was fine at lower speeds.

K

geoffus · Oct 29, 2021

Jobsworth said:
Now, don’t take this the wrong way, but I’ve seen aftermarket scan tools get left and right muddled on mercedes cars before. Just to confirm that you are on the right track I would swap the sensors left with right. Just to be sure you aren’t barking up the wrong tree

Good idea, I will remove the right hand sensor to see if it stays the same.
From what I've read recently it seems common for the reluctor ring to corrode and cause a similar issue.

johnsco · Oct 30, 2021

Reluctor rings can both corrode and crack.
I had a cracked one some years ago that was causing abs and engine management problems.

m80 · Oct 30, 2021

I would do a simple check on tread depth, just to eliminate.

Petrol Pete · Oct 30, 2021

As m80 says ^^^ takes minutes. Years ago on my 1996 Vectra company car fitting a new tyre to just one side (puncture) upset the crude ABS , fitting a new tyre to the other side cured it.

Unlikely to be your issue , but worth a quick look.

geoffus · Oct 30, 2021

Took the wheel hub off and found the what I think is the abs sensor plate, it has a crack and the cv joint it fixes to is all badly corroded. I will get a cv repair kit and order a new sensor plate. The outer cv is so badly corroded the sensor plate is loose.

geoffus · Nov 3, 2021

Finally solved my ABS problem so if anyone has similar issues, this is what I found.
The wheel bearing has a magnetic encoded seal, this replaces the traditional reluctor ring that's fitted to drive shafts.
When I took the front knuckle off I could see the bearing seal was damaged, I did think about just replacing the bearing for around £40 plus getting it fitted with a press, but as its been off the road for around a week I phoned Mercedes Edinburgh and they sent a complete Knuckle for £240, including next day delivery.
Took about 1 Hour to fit, took it for a test drive and its fixed, success.
The left hand drive shaft was very rusty, so may have caused the damage to the seal, I have cleaned all the rust off this and painted it. It was also fitted with a new centrifugal seperator.
All the codes were cleared and not it runs as new again, so the wife has got her car back, she is pleased although she did tell me to take it to a garage to fix it after 5 days of getting nowhere.