I had rear right sensor failing and then failed permanently. It was eroded a bit by rust flakes. I changed it and the error happened only one more time after clearing, and then went away.
HOWEVER, few days later front left sensor started to be reported. So I thought that's suspicious but I changed the sensor anyway. This one didn't have any rust on the shaft ring.
Replacing it didn't help. Actually now the error shows up right after the ignition on.
I must say that I had other corrosion issues ever since two years ago I shipped the car in the closed container over the ocean. Do not recommend... Some nuts are visibly rusted in the engine bay. Inside the cabin, downshift paddle stopped working for a while. And to this day volume button sometime dials last number instead of changing volume.
Anyway, there are two types of sensors and on my 2011 135i I believe there is newer version (which is more difficult to test). The
old one would change current depending on proximity and new one is 1-wire digital signal.
I am yet to find find right method to confirm that any of the sensors work... Maybe they have to be tested when installed.
Another symptom is that during tight turn and braking ABS thinks I am skidding and the pump starts doing abs intervention.
Did any of you had that? I have M3 steering rack so it maybe this is due to yaw/steering ratio mismatch..
So I don't know. Maybe one of the DCS power stage is failing and not providing enough current to the sensors (since the error moved from one wheel to another).
Or both sensors were failing in the same time. One due shaft rust and second maybe due to wiring rust or just itself.
Freaking mystery.
EDIT:
1. I believe the two cheap new Chinese sensors I bought are dead as well. So I bump up the theory that it was just two sensors just failed more or less at the same time.
2. The protocol might be the same as in F82, as suggested by E90 Bentley manual:
Pdf:
I need to look more into this. I think rear sensors are simpler and use a reluctance ring, while front ones are more precise and measure magnetic field.
3. I connected the front (OEM - maybe faulty) sensor through 147ohm resistor to a power supply and measured the voltage drop using scope. There is a waveform generated every 165ms
and looks like this (7-14mA):
Wave doesn't change even when waving a magnet in front of the sensor.
4. Rear, OEM presumably faulty sensor doesn't produce the square wave. Just constant 7mA draw and waving a metal in front of it does fix it.
5. One of the chinese sensors that I have is producing the same square wave, except every 150ms and it can have a big spike when bringing magnet very close:
6. So I believe there are two types of front sensors (even though they look the same).
34526870075is active with the protocol example shown on the scope above and
34526762465 is PWM responding directly to the reluctance ring. The latter is present on crappier-engine cars - according to realoem (presumably without hill hold feature). The 34526870075 works with magnetic bearing plate and the other with reluctance ring. Rear axle has reluctance ring and probably just one version of the sensor.
