[nsjames]

Originally Posted by Efthreeoh

I just got to thinking you may not have a complete understanding of the system. The sensors are two-stage, which allows the CBS system to estimate the wear on the pads. There is an algorithm that starts out at zero (i.e. reset) and progresses the wear estimate based on a standard wear calculation. Once the 1st stage of the sensor is tripped then the CBS has an actual count of miles from reset to 1st stage miles and uses those data the predict pad wear going forward. The errors that owners get from replacing brakes is they inject data into the algorithm which is outside the parameters of the data it is expecting. If an owner follows the correct procedure when replacing the brakes, which includes a new sensor and pads with a full reset of the system they do not get the CBS out of sync. Keep in mind the algorithm is counting time, not just wear sensor triggers.

This is why I recommend replacing the sensor with new pads regardless of the wear or age of the old pads and sensor. Unless you have visually inspected the sensor and measured it's resistance (resistance changes between the two stages - and the resistance values has been published on E90 Post) you can't be sure the system will not get out of syncronization from what it expects to happen regarding pad wear. The best practice is just to replace the sensor with a new one along with the new pads and reset the system.

the other issue with reusing the sensor, it's been in there for a while and is fragile.

I left my rear sensor and just reset the CBS, then the sensor wire broke 15K miles later and freaked all of it out.
I replaced the sensor with a new one and played hell trying to get it to reset properly. Had to dead short the pins and reset it before it would take the new sensor and stop flashing brake warning lights at me.

so for the $15 a sensor costs, just do it, and reset the system.

[nsjames]

Originally Posted by ducatiti

I am more worried about the warning light problems after resetting the system.

I inspected my new sensors, and there seems to be a copper/metal in the opening or the part where you insert it to the pad. Am I supposed to install it with it on?

photo?
there's a metal shim that holds it in the pad, is that what you're referring too?

You shouldn't see exposed copper on the face of the sensor, at least not on a brand new one.

the sensor is basically a wire loop. The computer measures the resistance. When the sensor makes it to the rotor, the rotor rubs away the face of the sensor and eventually rubs through a piece of copper wire embedded in it. When that circuit goes to infinite resistance, the car knows that the wire has been worn through and that's how it knows the pad wear.

[ckev70]

Originally Posted by nsjames

photo?
there's a metal shim that holds it in the pad, is that what you're referring too?

You shouldn't see exposed copper on the face of the sensor, at least not on a brand new one.

the sensor is basically a wire loop. The computer measures the resistance. When the sensor makes it to the rotor, the rotor rubs away the face of the sensor and eventually rubs through a piece of copper wire embedded in it. When that circuit goes to infinite resistance, the car knows that the wire has been worn through and that's how it knows the pad wear.

For additional reference:
The sensor shows metal which clips into the brake pad
https://www.fcpeuro.com/products/bmw...or-34356789440


@ 9:30 it shows how the sensor clips into the brakepad
https://www.fcpeuro.com/products/bmw...6789440#video0

[Efthreeoh]

Originally Posted by ducatiti

I am more worried about the warning light problems after resetting the system.

I inspected my new sensors, and there seems to be a copper/metal in the opening or the part where you insert it to the pad. Am I supposed to install it with it on?

A new sensor has a brass u-shaped spring clip in a groove in the plastic body, which fits into the U-shaped opening in the pad material. The sensor snaps into the pad.

[ducatiti]

Thanks all. Installed my Zimmerman coated rotors and Akebono Ceramic Pads on all four corners. Installed new sensors and bled the brakes.... Reset the system with no errors at all.

[John 070]

I replaced them on the 335i, front rear, because they were cheap (OEM around $13-$15). On my Lexus, I decided to just reinstall the old (Lexus OE is like $120+!! aftermarket $9). I almost wish cars didn't have these, not really useful to those of us who inspect our brakes when we put snow tires on/off. The BMW dealership ripped my brand new sensor wire when they are doing the alignment on the rear right wheel.