[asiemers]

I just recently got my front pads and rotors replaced due to warped rotors, the front sensor wasn't triggered at all as far as I know. My service info says theres only 5k miles left on the brakes so I'm assuming it was the rear brake pad sensor has been triggered although I got no warning. Is it possible I could reset the brake service indicator if I only replace the rear pads and sensors and leave the front sensor? Assuming the front sensor was never triggered before I got front pads.

[Efthreeoh]

What I'm about to write assumes that the brakes have been properly maintained prior to you owning the car. The CBS reports on the estimated brake life of each axle independently, so you can go to the CBS maintenance menu and see which axle has what ESTIMATED life is left for each axle. The mileage is an estimate only and does not indicate when the pads actually need replacement. When the red "BRAKE" symbol lights in the gauge cluster and stays on whenever the engine is running and the handbrake is not engaged (it's the same one that lights when the hand brake is on) that's the indication that one or both of the brakes (axles) needs replacement. The CBS will show -- on the maintenance menu for which axle needs replacement. Until the "BRAKE" light illuminates you don't need to do anything.

The CBS can estimate the brake pad life remaining because the sensors are dual stage. The first stage when reached, gives the CBS an actual mileage data point of how fast the brakes are wearing. The CBS estimates pad life remaining even before the 1st stage is reached just based on mileage; when the 1st stage is reached the CBS then updates it calculation. However the system is not perfect and assumes a consistent use of the brakes; meaning if you change commutes over a long period of time the CBS may over estimate or under estimate the pad life. For instance if you bought a used E90 that the previous owner drove in the city and used the brakes a lot and got though the 1st stage of the sensor, and then you bought the car and drove it mostly highway, the CBS might over estimate the pad life. But none of it really matters since when the 2nd stage of the sensor(s) is reached, the "BRAKE" light comes on and is indicating one of the axles needs new pads.

Now the issue you are going to have with your front brakes if the shop didn't replace the sensor when it put new pads in, is the CBS is going to under estimate the front pads life because it has been calculating the brake pad use since the last sensor was installed. Correct practice when replacing BMW brake pads is to always replace the pads and sensors as a set and reset the CBS for the axle that the pads were replaced on now matter how unused the old pads were.

Bottom line is you don't need to replace the pads until the indicator comes on.

[mob17]

Wondering if you could help me. I just replaced all discs pads and sensors and now CBS is showing 18k left on brand new brakes? Will it correct itself over time?

[Efthreeoh]

Originally Posted by mob17

Wondering if you could help me. I just replaced all discs pads and sensors and now CBS is showing 18k left on brand new brakes? Will it correct itself over time?

Yes if whoever did the brakes reset the CBS correctly. You guys need to understand the CBS is just an estimate. It doesn't trigger the light that indicates the pads need replacement. The sensors trigger the light.

[QUiKSR20]

So if we were going to replace the pads ( Front & Rear ) would the procedure be :

- Replace Front Pads w/Sensor
- Replace Rear Pads w/Sensor

Reset Brake Service indicator ( Front & Rear ) :

And thats it?

Doing brakes on my E90 this weekend for the first time, Lights not on yet but just doing some maintenance ( pads are real low ).

[Stevec C.]

i've had problems where after replacing the brake pad sensors it still DOES NOT reset the warning. but after digging into this forum, there was one post that suggested to let the engine run for about a couple of minutes before doing the reset. that DID the job for me.

in short, after replacing the brake pad sensor(s) or just doing the jump-wire trick, you cannot reset the computer right after you turn the engine on. start the engine, wait a couple of minutes, then do the reset. it worked for me.

this forum has been invaluable for me. thanks everyone.

[ferocity02]

I think the mileage on the display is calculated based on your driving habits and whatever BMW though was reasonable. The sensors don't continuously measure wear. In fact with new pads the sensors won't even touch the rotors until the pads are worn down a good amount. Once the pads reach a certain thickness then the sensor is tripped and I guess it gives you a warning on the dash.