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-   -   BMW brake pad worn out, but iDrive shows lots of life left (https://www.team-bhp.com/forum/technical-stuff/248647-bmw-brake-pad-worn-out-but-idrive-shows-lots-life-left.html)

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.)



Apart from the routine visual inspections, is there any measure in place from preventing a re-occurance?
A noteworthy piece of info is that I’d gotten the alloys and callipers painted in early Jan. Could mishandling the callipers be a reason for the sensors by any chance not showing a correct reading?

I really do need to get to the bottom of this and atleast find out a reason for the car not pointing this out to me (when it’s supposed to).

All inputs humbly welcome!

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.

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?

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:

https://www.team-bhp.com/forum/long-...ml#post3505665

My understanding of this as seen during XUV 5OO's brake pad change -

Brake wear sensor needs the pad to wear out to a level that it contacts the rotor and closes the circuit - so it's only meant to be a fail safe perhaps for compliance in export markets , the correct method is visual inspection.

I don't think the electronics would know even if the wear sensors are disconnected.

Oh! Isn’t that just losing all purpose of a sensor in a way?!
Anyhow, even with the passive TPMS like you’ve mentioned I’m guessing it’s just better to leave these electronic alerts as a guideline at best. My concern was the presence of a sensor and that in a way, malfunctioning.

The car was braking really well on a recent Goa-Pune drive and I didn’t notice anything unusual on that front. I’m sure there must’ve been some(if not a lot of) noise given the scrapping that the disc has been subjected to. Just wasn’t attentive enough on it.

Yes. However, the front pads are in good shape and only the rear ones have been worn out. Since this is a pre-owned car, I’m guessing the front pads must’ve been replaced not too long ago, and I’ve just not paid enough attention to this.

Yes, I think so too now. Thanks.

Like mentioned in one of the posts, the I drive is only an estimate of the actual life of the pads. It’s a handy tool nonetheless. The default is 50k km at the time of replacement in india. It drops down as you drive but sometimes during a service if they do a reset then the car comes back with a reset value at 50k km. That’s the time the calibration goes for a toss. Then the system takes a long time to recognise the real life left in the pads, and sometimes it never does, that’s when you get a drop of 20-30k km overnight. But still you do get a couple of days to plan your replacement. Outer pads are easy to check just with your mobile flashlight through the alloys. Inners can be checked while the vehicle is on a lift only.

Have faced this issue multiple times with my X1. iDrive shows 2000 kms left for replacement of brake pads whereas on inspection break pads are worn out and noise was there while breaking. Visual inspection would be the way to go.

The system in new Volvo cars also works in the same way, however, it does point out the tire pressure issues even at low speeds. But the car does need to be moving for it to determine that the pressure is low in a tire. It works by measuring the rotational speed and comparing it with the other tires.
Not the best system but it needs no additional hardware so the manufacturers like it very much.

It is similar in my Q5. The previous owner (a very good friend) told me to get the pads replaced in the service due 4 months after I had bought it. I had made an exhaustive list of things to be checked and replaced during that service already, including the brake pads. The owner of the FNG who had been servicing it since the warranty expired checked the MMI and told me all's ok with the pads. I told him to change them nonetheless. The pads were near end of life and in retrospect, I recollect hearing a faint noise sometimes from the front right side under heavy braking prior to changing the pads which went away afterwards. Couldn't notice any improved braking though

Somehow never faced this issue on F48 X1 and brake pad wear sensors have been pretty accurate for both front & rear. They only pop up warning when remaining pad life is 4,000 Km and BSI allows to have it changed once you reach 2,000 Kms mark. No question asked.

You can install an active TPMS like SensAiry for 4 tyres and that would solve your problems by giving real time air pressure and even temp.

Amazon Link.

Note: Not associated with them.

All modern BMW now come with active TPMS.

iDrive has shown the opposite to me, got a warning saying that the pads were fully worn and that I should drive slowly to the nearest service centre, when the pads actually had 80% life left!! So it's definitely a mixed bag.