Arrie

So, driving last night and suddenly I get all of my driving aids disabled. No ABS brakes, no Distronic, no Pre-safe Brake, No Lane Keep Assist, No Blind Spot Monitor, No Hold function, no Hill Hold and the CEL was on. It is quite devastating at first when this happens as the whole car seems to have "broken".

Connected the iCarsoft scanner and as the CEL was on and as it is the second module on the list I just read that and it shows the front left wheel speed sensor has gone bad. This same message was at several modules so it was an easy decision to go visit my local MB dealer for the part. Changed the sensor and reset all errors in various modules and problem solved.

It is just amazing how this one sensor takes out all of the driving aid functions of the car.

BOTUS

the merc instructions are to always change as a pair (don't know why)

they all die, I didn't wait for a breakdown and just fitted all 4 - same year all within 6 months six owners with w221s on big UK forum all did the same, then inside the next two years we saw 4 on this forum... and years since see quite a few others here.... designed to fail

DaleB

Lucky you. Mine turned out to be a bad ABS/ESP control module, all of my wheel speed sensors were fine. But yeah, that module NEEDS to know exactly what each wheel is doing at all times, and it is used for a lot of functions on the car.

Arrie

Yeah, signal is used in places but what the heck has the wheel speed sensor to do with Blind Spot monitor or the Hill Hold? I forgot to mention also the Electric Emergency Brake was out. Why this also as with cars with mechanical foot operated EM brake it does not disable for any reason.

Arrie

I did buy two sensors to do the right side too…

w126w221

BOTUS, what year is your 221?

DaleB

If the system or feature in question uses the brakes at all... or needs to know the exact speed or trajectory of the car... the it needs the wheel speed sensor data. If that data is incomplete or can't be trusted, then the entire thing is effectively off line.

Hill Hold & parking brake both use the ABS module to activate brakes. Blind spot monitor, I don't know... unless the car can also intervene to avoid a collision, in which case, yeah, it would use brakes for that.

Arrie

It is 2013.

BOTUS

2006, all the six in that year were 2006 I believe, then when u see them pop up here its the usual round of the next year's batch failing, mileage is nothing to do with its "special metallurgy", but these days they moved to random software "extras"