[rangeseeker]

Okay so I got my front brake pad warning (on a car I'm about to sell), ordered the pads and went to put them on. I already put the new ones on, but looking at the old ones they have a ton of meat left. Why did I get a warning light if there's so much left? Is this really low enough to justify replacement? Also, the sensor looks to be in perfect condition. Am I missing something?

[Billfitz]

Probably a faulty sensor, internally so you can't see it.

[Z K]

Besides tripping the sensor, there's also a mileage count down for the brake pads. That counts down regardless of the sensor. If you have a lot of miles on your car, it can ask for a replacement because of that. Since you say your car is a 2016, I don't think you'd have that many miles to trigger it... May be just a faulty sensor.

[MacklinUSOB]

You definitely got your warning prematurely. The sensor is supposed to trip when it makes physical contact with your rotor on that little plastic nub you pictured, clearly it hasn't. It must have tripped due to some other damage or defect in the sensor as mentioned above.

As far as whether it's worth it to change them, you already said it was a DIY so you didn't lose a heap of money doing it. If you could rewind time I would say just replace the sensor and sell it, but since you've already done the work it is kind of a moot point.

[Billfitz]

Originally Posted by Z K

Besides tripping the sensor, there's also a mileage count down for the brake pads.

There is, but it's only a guesstimate, as there's no mechanism by which the system measures the remaining pad thickness. AFAIK the only way the replace pad warning comes up is when the sensor is triggered or if the sensor is faulty.

[Orion4]

Did you get the warning or was it the Brake service alert on the I-drive? The I-drive alert had to be reset on my when it came on at 35K miles. Im at 112,400 today on original pads and rotors. They are getting very close though.

[Z K]

Originally Posted by Billfitz

There is, but it's only a guesstimate, as there's no mechanism by which the system measures the remaining pad thickness. AFAIK the only way the replace pad warning comes up is when the sensor is triggered or if the sensor is faulty.

I've gotten the brake pad replacement warning come up when the "miles to brake service" counts down to zero. This is on my track day car so I guess the car felt there was accelerated wear from hard braking. I know the brake sensor was not triggered because I had removed them from the pads and zip tied them. To reset the counter, you still need to replace the sensor even though it's not worn.

There are two triggers for the pad replacement, one is mileage based, the other is sensor triggered. You'll see references to the mileage based brake pad warning on other BMW forums.

[MacklinUSOB]

Originally Posted by Z K

I've gotten the brake pad replacement warning come up when the "miles to brake service" counts down to zero. This is on my track day car so I guess the car felt there was accelerated wear from hard braking. I know the brake sensor was not triggered because I had removed them from the pads and zip tied them. To reset the counter, you still need to replace the sensor even though it's not worn.

There are two triggers for the pad replacement, one is mileage based, the other is sensor triggered. You'll see references to the mileage based brake pad warning on other BMW forums.

This is weird because I'm about to swap my 4th sets of pads up front reusing the same sensor i got with the car, never got a warning light. I checked iDrive this evening and it says 3100 miles. I'll see how it changes after my next track day.

[rangeseeker]

Originally Posted by Billfitz

Probably a faulty sensor, internally so you can't see it.

Originally Posted by Z K

Besides tripping the sensor, there's also a mileage count down for the brake pads. That counts down regardless of the sensor. If you have a lot of miles on your car, it can ask for a replacement because of that. Since you say your car is a 2016, I don't think you'd have that many miles to trigger it... May be just a faulty sensor.

Originally Posted by Orion4

Did you get the warning or was it the Brake service alert on the I-drive? The I-drive alert had to be reset on my when it came on at 35K miles. Im at 112,400 today on original pads and rotors. They are getting very close though.

I got the warning light and the mileage "past due" warning thing. This is on a 2013 328i thats at 130k miles. They are OEM pads but I don't know if they're the originals. Either way, thats a lot remaining on them.

[Fliplegend]

Just did my fronts a few weeks ago. This is what they looked like. This was 200 miles past the count down. The thicker ones are the outer pads. From what I've read, you have about 2K miles after the count down expires. That's if you can make it that long with the car constantly nagging.

[Billfitz]

Originally Posted by rangeseeker

I got the warning light and the mileage "past due" warning thing. This is on a 2013 328i thats at 130k miles. They are OEM pads but I don't know if they're the originals. Either way, thats a lot remaining on them.

That means you got a warning based on mileage, not by the sensor being tripped. It's easy to know which is which without looking at the pads. If the sensor hasn't been tripped you can do a reset. If it has been tripped you can't do a reset until you've replaced the sensor.

From what I've read, you have about 2K miles after the count down expires.

Maybe, maybe not. As is usual with BMW it errs on the side of caution, so the mileage remaining number tends to be conservative. Still, it's better not to pull a Kramer trying to find out how far you can drive after the tank reads empty. The price paid for waiting too long to replace worn pads is damaged rotors.

[Fliplegend]

Originally Posted by Billfitz

That means you got a warning based on mileage, not by the sensor being tripped. It's easy to know which is which without looking at the pads. If the sensor hasn't been tripped you can do a reset. If it has been tripped you can't do a reset until you've replaced the sensor.

Maybe, maybe not. As is usual with BMW it errs on the side of caution, so the mileage remaining number tends to be conservative. Still, it's better not to pull a Kramer trying to find out how far you can drive after the tank reads empty. The price paid for waiting too long to replace worn pads is damaged rotors.

Agreed. Just wanted to let others know how much leeway you have once the sensor is tripped. Naturally doing a track day after the sensor is tripped would be a terrible idea but in my case I drove for another week and clearly could have driven much longer before it was metal on metal.

[Billfitz]

While on the subject thanks to your picture I see how the sensor works. You can see two copper conductors revealed where the sensor contacted the rotor. I'd say before it contacted the rotor there was a copper trace that connected those conductors. The system checks the continuity, and when there is no continuity because the conductors are no longer connected the count down begins. This would explain why once tripped the sensor has to be replaced. It also explains how you'd get a false positive. A break in the sensor wires anywhere would also result in no continuity.