There are a couple of sensors on the brake assemblies; pad wear sensor which are sacrifical by design and need to be replaced once triggered,
and the pulse sensor which measure the rotation speed of each wheel and feeds it into the ABS controller. If the pulse sensor is damaged then the ABS system can't figure out what is happening and disables itself, the pad wear sensor plays no role in the ABS that I am aware of. But I have been wrong before (but don't tell anyone).
Back to the pad wear sensors, there are normally only two of them, usually on diagnoally opposite wheels. Just because one has gone, doesn't mean that you need to change both of them.
Just to add to Brett's reply...
Inspect the rear of the rotors as the fins the the sensors operate from can often get clogged with debris from the pads, or even accrue some rust !! If this is so then give them a massive clean with a tooth-brush or similar/harsher !!
Eso es todo! Please press the "REP" button if you are happy with your response/answer...
i played with the tcs plug yesterday and the light went out for about a hour (didn't play up till the apprentice look at it for a previous problem ) will have a look at the rear brakes when i do front this week
it actually dose in the wet if its on it'll go off for the slightest thing but same conditions with it off and there is no slid spin or what so ever but the other day b4 it broke it locked and put me sideways of a round about lucky i was quick or i would of had another problem (replacing the car)
any way i bought new dics for the front they are of the solid type like the ones on there now only paid $49 each and in the process i have found a spare parts specialist for bmw and the merc the maf unit is only $305 and the advice is freeeeeeeee haluia
would just like to support Dabsy on the rusty abs fins theory as that turned out
to be my problem way back on an e28 rear, turns out the sensor just cannot
read the fins,also last week the brake pad warning light came on on wife,s e36
problem turned out to be a very small cut in the sensor wire,I guess enough to
allow damp to reach the copper part of the wire & trigger the alarm,replaced
sensor from GSF £7.oo & problem fixed.
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