BMW idrive: Inaccurate brake pad wear information

The F25 has two sensors for brake pads. The rear pad being on the rear right wheel. Surprisingly there has been no warning from the car.

BHPian humbleroadster recently shared this with other enthusiasts.

A recent visit to an FNG in Pune has been very interesting. I was there to change the battery since an onboard voltmeter test showed a low reading. And sure enough, after a local check it was due for change.

That out of the way, what was also pointed out by the team was a heavily worn out rear disc. This was predictably because of no life left over on the rear brake pad on the rear right wheel.

The F25 has two sensors for brake pads. The rear pad being on the rear right wheel. Surprisingly there has been no warning from the car. The rear left wheel also had some life left on the pads, consequently leaving the disc unharmed. Needless to say, I’ve changed both the rear discs and pads now.

Infact, on the morning if the change, the Idrive showed a good 30,000 kms to go before a change.

There was a little life left on the inner rear right brake pad, but the outer had no pad at all! The top most pad in the snap below is the outer pad on the right wheel. Also, a pretty uneven wear out IMO.

Rear apart, the front pads are in great condition. (Photo below shows all four rear pads.)

Here's what GTO had to say on the matter:

I learnt a long time back that the iDrive data is merely a "suggestion" and not the last word. The brake wear sensors aren't accurate at all. Also, IIRC, the km countdown for them can be manually set.

It's like the F10's stupid TPMS system that detects flats or low tyre pressure only above a certain speed. In Bombay, it has warned me of low tyre pressure only on the Sea Link (~80 kmph). Not real-time pressure monitoring at all. I suffered a puncture recently, but the iDrive didn't have a clue because it was at a low speed! Stupid feature depends on the ABS wheel speed sensors, and not actual pressure sensors on the wheel + tyre.

Here's what BHPian Hayek had to say on the matter:

Interesting and disconcerting experience. I have observed that the X3 brake wear indicator is not linear - it guesses how much wear has taken place and gives and estimate - and then the sensor gets triggered and the estimate drops dramatically. Just had that happen where my rear brake sensors which were showing 25,000 km (iirc) dropped to 2000 km literally overnight. So that’s something I have gotten used to - but of course I have no idea if it is working correctly. Will take the car to the workshop in about a month when it should drop below 1000 and see what has happened. Did you get any indication in terms of braking efficiency or noise?

Here's what BHPian androdev had to say on the matter:

Unfortunately this is not such a rare thing, if you understand why. Like GTO mentioned, iDrive info is only as reliable as the sensors used for gathering such information. In this case, there are 8 brake pads with just two wear sensors and uneven wear can fool the iDrive into thinking all is well. However brake pads are designed to give out of a metal-scraping sound once the wear limit is reached and we must pay attention to such sound. This is how it works in analogue world ;-) It also helps to remember that brake pads on these cars will require replacement after 18K-24K km.

Here is a similar experience from my S Class thread.

Read BHPian comments for more insights and information.