[BMWUltimateDriv3r]

However I just got them replaced 12k miles ago. So it would be a 26k miles interval. That cant be right can it? My first set lasted 68k miles.

[fun2drive]

There is no sensor that is telling the computer the front brakes need replaced in XXXXX miles. The computer algorithm is what is doing this. The front sensor on the driver's side and rear on the pass side only comes on when the pads make contact with the sensor completing the circuit.
My guess is your car's algorithm is total messed up and I would do two things, verify the pads have lots of life (sticking caliper can play havoc with your pads) and reset the computer if your pads are good...

[BMWUltimateDriv3r]

Can you show me pics where I can manually verify?

[Meeni]

...

[Efthreeoh]

Originally Posted by fun2drive

There is no sensor that is telling the computer the front brakes need replaced in XXXXX miles. The computer algorithm is what is doing this. The front sensor on the driver's side and rear on the pass side only comes on when the pads make contact with the sensor completing the circuit.
My guess is your car's algorithm is total messed up and I would do two things, verify the pads have lots of life (sticking caliper can play havoc with your pads) and reset the computer if your pads are good...

Actually there is a sensor that does help calculate the pad wear and predicts the mileage remaining. The brake pad sensor on the E9X is a dual stage sensor where two wires are embedded in the plastic casing. The CBS uses a predetermined algorithm to determine an estimated mileage of remaining pad life until the 1st wire is broken. Once the first wire is breached in the sensor, the CBS now has actual data of how long and how many miles it took to wear the pad down to the point where the 1st wire hits the rotor. The CBs can then use that information to adjust the algorithm calculation and give a more accurate prediction of when the pads will be spent; when the second wire breaches the rotor and triggers the "brake" light on the gauge cluster. The estimated pad life does assume a somewhat constant use of the brakes, so if the driver changes his driving habits or changes his commute (say from mostly highway to mostly city) the estimate may be somewhat inaccurate. This is not a problem however since when the second wire breaks the pads are spent and need replacement and the car correctly indicates so.

OP, don't try to out guess the system. If the brakes were correctly serviced and a new sensor installed, the car will tell you when the pads actually need replacement.

[Efthreeoh]

Originally Posted by Meeni

This countdown is for a brake inspection, not the brake wear sensor. Do the inspection, reset the countdown.

This is not correct; it is not a count down to brake inspection. It is an estimated mileage remaining on the brakes. You really don't need to inspect the brakes (unless a problem develops like a sticking caliper that wears out the pads prematurely).

[CaptChaos]

Originally Posted by Efthreeoh

Actually there is a sensor that does help calculate the pad wear and predicts the mileage remaining. The brake pad sensor on the E9X is a dual stage sensor where two wires are embedded in the plastic casing. The CBS uses a predetermined algorithm to determine an estimated mileage of remaining pad life until the 1st wire is broken. Once the first wire is breached in the sensor, the CBS now has actual data of how long and how many miles it took to wear the pad down to the point where the 1st wire hits the rotor. The CBs can then use that information to adjust the algorithm calculation and give a more accurate prediction of when the pads will be spent; when the second wire breaches the rotor and triggers the "brake" light on the gauge cluster. The estimated pad life does assume a somewhat constant use of the brakes, so if the driver changes his driving habits or changes his commute (say from mostly highway to mostly city) the estimate may be somewhat inaccurate. This is not a problem however since when the second wire breaks the pads are spent and need replacement and the car correctly indicates so.

Great info, I never knew that detail.

[jeffro535]

Interesting info. I recently moved and my daily commute changed from about 25 miles each way, typically hard high speed, to 8 miles each way, somewhat more sedate, and the front pad indicator went from due in 9k to due in 12k.

[Dark_Knight_335]

Had a similar problem. Dealer, after 3 visits and resetting the sensor (and having it happen 3 times), they finally replaced the brake sensors with "upgraded" brake sensors. No problems since. Might want to ask them about this.

[PhaseP]

DO NOT try to reset the brake service interval from your computer if it had been already reset once. Because if you had already made to the 1st stage of the brake wear sensor, when you reset it, you will get a red brake service light with -9000 miles overdue service warning. This will only clear if you put a brand new wear sensor and reset again (or trick it by shorting the sensor wires as if new sensor was there). After a reset, the computer assumes new brake pads and new sensor had just been installed. If it finds a sensor that is already at stage one, it complains and puts the red light on.

My experience, the brake service interval that computer shows dynamically gets updated as you drive. I had my brakes changed at 70K miles. After reset, computer showed 20Kmiles left. Then after a few months it started showing 31Kmiles left. Now it shows 38K miles left. So it appears it initially estimates worse case usage, but then adapts and readjusts as you use the car.

The most reliable estimate, as mentioned earlier in the thread, will come after you hid the 1st stage on the sensors.

Just leave them alone for a month or 2, then check them again.


See here for the sensor internals
http://www.e90post.com/forums/showthread.php?t=981050

[Efthreeoh]

Originally Posted by PhaseP

DO NOT try to reset the brake service interval from your computer if it had been already reset once. Because if you had already made to the 1st stage of the brake wear sensor, when you reset it, you will get a red brake service light with -9000 miles overdue service warning. This will only clear if you put a brand new wear sensor and reset again (or trick it by shorting the sensor wires as if new sensor was there). After a reset, the computer assumes new brake pads and new sensor had just been installed. If it finds a sensor that is already at stage one, it complains and puts the red light on.

My experience, the brake service interval that computer shows dynamically gets updated as you drive. I had my brakes changed at 70K miles. After reset, computer showed 20Kmiles left. Then after a few months it started showing 31Kmiles left. Now it shows 38K miles left. So it appears it initially estimates worse case usage, but then adapts and readjusts as you use the car.

The most reliable estimate, as mentioned earlier in the thread, will come after you hid the 1st stage on the sensors.

Just leave them alone for a month or 2, then check them again.


See here for the sensor internals
http://www.e90post.com/forums/showthread.php?t=981050

This is perfect advice. Just let the CBS sort itself out; it's just an estimate of how long the pad life is. It really doesn't matter what the estimate is because the system has a built-in positive identification of when the pads are at the minimum wear spec. Bottom line is when the pads are truly in need of replacement the car will let you know.

[Efthreeoh]

Originally Posted by CaptChaos

Great info, I never knew that detail.

The older BMW pad wear system (they've had it since the mid 1980's), was a simple one-wire loop sensor, and when the light came on the pads need replacement. With the advent of BMW's CBS maintenance system, I guess they decided to have the CBS be able to predict estimated pad life (like the other maintenance items). The problem is they don't do a good job at explaining how the system works. Some people don't understand that the "sensor" is consumable along with the pads, which makes it confusing.

[Meeni]

Is there anyway to "rollback", in the case someone would have incorrectly reset the indicator ?

[alexwhittemore]

Originally Posted by Meeni

Is there anyway to "rollback", in the case someone would have incorrectly reset the indicator ?

No. But because the second wear indication on the sensor is a hard and fast "brakes need to go NOW" indication, you can just wait for that. The estimation of life remaining won't make any sense until then, though.