W204 ESP,ABS etc lights

[sceh]

W204 diesel 2011 50K miles.
I get the ABS, ESP, DSC lights on randomly and when it happens the ECO light goes out and won't work.
Carsoft tells me there is a fault code C113000 L6/4 right rear electrical fault. However, the wheel speeds are perfect.
The car is left hand drive so right rear is which wheel (imagine you are in the driving seat - is it behind you or the other one?)
I also get U140D00 unreasonable wheel speed but this is no surprise as well as D40C (no CAN data etc)
If I clear the faults, all is ok, ECO works and this can last ten miles or 100 yards before I get the erros again. If I stop and restart the errors often disappear.
ANY ideas why this can happen?
I know a STAR visit might help but I am wary
I have changed the rear wheel speed sensors multiple times in the past but It could still be a duff sensor and since the speeds read OK, how can I tell?

I am lost

 

[mersum1es]

rear reluctor ring rotten. Gives a signal but fails one then, more frequently then

 

[sceh]

an I see this via visual inspection? Seems odd given the mileage and it is garaged and rarely out in the rain and mud

 

[Blobcat]

an I see this via visual inspection? Seems odd given the mileage and it is garaged and rarely out in the rain and mud

Sitting around gives plenty of opportunity for corrosion to work away.

 

[Snake Charmer]

I replaced a reluctor ring on my S211 last week. I could not remove the sensors easily to swap from side to side as they were corroded in so l read their resistances and as they were the same, changed the reluctor ring that side.
The reluctor ring was sat in the suspension upright against the wheel bearing having been pushed off the CV hub by corrosion on the driveshaft.
My driveshafts show no corrosion prevention from the factory, 21 years and 125k miles the corrosion has formed an oxide layer that chips off and continued down under the reluctor ring.

 

[sceh]

The plot thickens.
Start the car, don't move it, clear all the faults with Carsoft and just now and again the three lights 'ESP,EBS,EBD) will flash on for about five seconds then dissappear.
So, this is nothing to do with wheel speeds (since they are ok), nothing to do with reluctor rings either.There are loads of posts about the right rear sensor etc but it is not this as people who change it soon find out.
Given the D40C, no CAN data and so on it points to a bad contact somewhere and by definition not at the wheel level or the sensor level.
Now I need to find it..

 

[sceh]

 

[sceh]

Checking around the net I find dozens of references to the 'right rear electrical fault' when this error message arises and the warning lights come on.
This alone is curious. Why would it always be the right rear and not the left rear especially when the wheel speeds can be read perfectly.
Simple - it isn't the right rear at all and nor is it anything in the chain of events up to the ESP module. It could possibly be a chafed wire but Mercedes build cars properly so this is pretty unlikely in the majority of cases. It is a bad contact

 

[sceh]

If a reluctor ring on WHEEL is cracked it theoretically makes no difference as long as it rotates. The Hall effect sensor detects the varying 'distance' from the sensor to the ring and nothing more and translates this into a signal which is read to give a rotation speed.
So, in general a reluctor ring will not cause a problem itself even if it is rusted unless the rust is so severe it alters the profile of the notches severely (in which case you probably need a new car..)
I can find no other technical reason why rings need to be replaced.
Hall effect sensors *could* be affected by shock which could reduce their magnetism so that the signal is poor though but you would need a lot of severe roads to so this

 

[EmilysDad]

.....
So, in general a reluctor ring will not cause a problem itself even if it is rusted unless the rust is so severe it alters the profile of the notches severely (in which case you probably need a new car..)
....

I replaced reluctor rings on my Smart Roadster due to rust ..... the rest of the car is relatively rust free

MB will/would only sell you a complete drive shaft

 

[sceh]

Next time, brush them really clean and treat with Jenolite

 

[EmilysDad]

Next time, brush them really clean and treat with Jenolite

There wasn't much left to brush