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Took my M340i in for the first service at 10,000 miles. The inspection record showed the rear pads were down to 4 mm (fronts were 9 mm). Asked the service advisor why the rears were worn so much and he said "we measure to the sensor, which will trigger and notify when the pads are worn to the point of needing replacement".
I wasn't completely satisfied by the response, so when I installed winter tires I took a look at the brake pads all around. All the pads were worn approximately 9 mm. However, the right rear inner pad has a sensor mounted to it and it protrudes approximately 5 mm from the metal backing plate. That explained the 4 mm measurement on the inspection report (9mm - 5mm=4mm)!
Now I'm curious why the wear sensor protrudes so far from the backing plate. It appears to me that it will trigger a signal long before the pads are worn out. I'm also curious why only one wheel has a sensor and why it is on the rear instead of the front. Anyone have any insight on this?
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