Graz

The clever computer on my 535d has been telling me how much mileage is left in my rear pads and was slowly creeping down. I know they're low as last time it was serviced my mechanic said there was only a few 1000 miles left on them.

So it got down to 500 miles on the computer and I'm ready to book it in for some new pads but it has now jumped up to 3900 miles until replacement. Most odd! I'll book it in anyway as better safe than sorry and all that but any idea why the sudden jump back in mileage?

May or may not be related but I gave the car a rare clean at the weekend using my pressure washer. Don't know if that upset it somehow.

john banks

On older BMWs the pad wear circuit can be in different states with part worn and full worn iirc. On newer ones the computer probably interpolates between depending on brake use. I would just look through the alloys but inner pads can wear unexpectedly and surprisingly on the rear with modern ESP.

ALi-B

iTrader: (1)

The pad wear sensors are just wires within a plastic insert thats placed in the brake pad, so it wears down and the wires metal contacts the disc.

One part of the sensor makes contact with the disc at 50% wear, and the other contacts at about 90%.

They can suffer water ingress, shorting the wire to earth, making the system think your pads are worn.

There is a bit more to it than that as the software does a bit of calculation to work out the mileages (something I need to read up more on to be frank, to explain their randomness). The CBS also throws a tissy fit if you re-use an old sensor.

Personally I wouldn't rely on them 100% and do a visual check (removing wheels if need be) ...quite often I've seen BMWs and Minis with a pad stuck in the caliper which has worn the one side down to metal ruining the brake disc, but the other pad with the sensor is fine.