Fixing brake pad warning light with BBK

[paradocs98]

Parts of this process have been posted here before, but I thought I would offer an update and bring it all together. I have a StopTech BBK front and rear on my E90 M3. I use the StopTech Street Performance pads for the winter/street season, and Pagids for the track--I just leave them in all summer. Neither of these pads will allow the OEM brake pad wear sensors to attach, so the sensors are just zip-tied out of the way, secured to the wheel-speed indicator cables (for ABS/DSC) that run alongside them.

Based on my understanding, the brake pad wear sensors run a continuous current, down one wire in the cable to the sensor itself, and then back up the other wire in the cable. When the brake pads wear to a minimum thickness, the sensor tab gets severed and the current from wire to wire is interrupted. This triggers the "Brake pads are at minimum thickness. Make an immediate appointment at your BMW center." message on iDrive, with the red-car-on-a-lift symbol in the instrument cluster. Also, annoyingly, when this occurs, the red "BRAKE" symbol continually appears in the instrument cluster, even when the parking brake is off.

So today I looked at the service menu in iDrive, figured out that the service message was being triggered by the front brakes and not the rears, and then took a look at the front brake pad wear sensors. I removed the front wheels and found the tied-off sensors, one of which looked like it had kinked enough to break one of the wires inside. I cut the sensor cable about three inches away from the sensor tab itself, threw out the sensor tab, then removed the exterior cable insulation from the end of the remaining cable to expose the two insulated wires inside. I stripped the insulation from the ends of the two wires, spliced them together and covered them with electrical tape, so now the current is again intact.

Important next step--apparently once the brake pad wear sensor has triggered or severed, the electronics "look" for a new/replacement brake pad wear sensor to be installed. The sensor comes as a unit, with the sensor tab attached to an approx 2ft cable that has a connector on its other end. This connector clips into a receptacle that rests in a small, rectangular plastic box attached to the inside of the wheel well/frame of the car. It's right there, accessible and easy to see on the other side of the strut once the wheel is off. So just cutting and splicing isn't sufficient--apparently once you cut and splice, you then have to "trick" the system into thinking that you've put in new wear sensor cables by opening the black box, unplugging the receptacle for the cable (it's the top one of the two that are in there--the other one is the cable for the wheel speed sensor) and then plugging it back in. Now the system thinks you've installed a brand new sensor cable after having put in new brake pads.

Once that's done and the wheels are back on, you can reset the indicator light in the instrument cluster and iDrive by following this procedure from e90post:
http://www.e90post.com/forums/showthread.php?t=51049

Follow it exactly, and it works like a charm! I was very excited and happy that I could get this figured out with help from here and e90post without having to make a trip to the dealer, and hopefully now it's an issue that won't come up again.

[My Schnell]

Great info!! Thanks!

[RickyBobby]

I'm only able to reset my brake counter once and it only adds a couple thousand miles. I'll have to try disconnecting the sensor to see if it lets me do a full reset.
How many miles does your reset counter read after you unplugged the sensor?

[MFKN3]

Thanks man!

Wouldn't unplugging and plugging it back in be the same as cutting the wires and joining them again? Just sayin'. Maybe it just takes a while for the i-drive to re-adapt to the signal? Otherwise, I think you can hard-reset through the instrument stalk in the cabin.

[Transfer]

This is great. Totally doing this next time my wheels are off. I've been living with the brake light on but it would be great to get rid of it. Thanks!

[paradocs98]

Originally Posted by RickyBobby

I'm only able to reset my brake counter once and it only adds a couple thousand miles. I'll have to try disconnecting the sensor to see if it lets me do a full reset.
How many miles does your reset counter read after you unplugged the sensor?

After the reset, my front brake service mileage countdown went to 2,500.

[paradocs98]

Originally Posted by MFKN3

Thanks man!

Wouldn't unplugging and plugging it back in be the same as cutting the wires and joining them again? Just sayin'. Maybe it just takes a while for the i-drive to re-adapt to the signal? Otherwise, I think you can hard-reset through the instrument stalk in the cabin.

The reason my "Brake pads are at minimum thickness!" warning illuminated is because the brake pad sensor cable was kinked and one of the wires inside broke, interrupting the circuit. So, even though the sensors were zip-tied out of the way and not connected to my aftermarket pads, the effect was the same as if the sensors were in place in the stock brake pads and the pads had worn down to their minimum thickness, severing the sensor tab and interrupting the circuit.

My sensor cables have been tied off out of the way for over two years now, but over time the bend in one of the cables finally snapped one of the wires inside. That's why the indicator light came on suddenly. If the wire had remained intact, then I wouldn't have needed to go through this process. By cutting and splicing the wires inside the cable, I was reestablishing the circuit, simulating a new or intact wear sensor. I did the same thing on the other side so that it wouldn't happen again. Plus, the computer probably wants the pads to be changed in front-front or rear-rear pairs. So if I had spliced and replugged the cable on only one side, and not unplugged/replugged the sensor cable on the other side as well, the service indicator might not have been able to be reset using the 'BC' button on the instrument stalk.

From what I understand, there are two separate types of brake service indicators. There's this type described above, where the wear sensor tab gets severed or crushed as the pads reach minimum thickness, creating the urgent "Brake pads at minimum thickness" message, with a red car on a lift icon in the instrument cluster. And then there's the more generic "Brake service due" message that is created solely by mileage/time, probably so the techs will check rotor wear, etc.

[MNm3]

When you unplugged the sensors, did you have to fire up the ignition before re-plugging them back in? Or can you just unplug and plug in without anything else??

[paradocs98]

Originally Posted by MNm3

When you unplugged the sensors, did you have to fire up the ignition before re-plugging them back in? Or can you just unplug and plug in without anything else??

Just unplug and plug back in. No ignition cycling necessary.

[ydoc]

Originally Posted by paradocs98

After the reset, my front brake service mileage countdown went to 2,500.

Anyone know a way after unplugging and plugging the sensor back in to get the service mileage countdown to go higher than 2,500 miles?

[bigjae1976]

I just cut off the end and splice the wires together close to the plug. Then cover in wire loom for protection.

[mid-corner fun]

Originally Posted by ydoc

Anyone know a way after unplugging and plugging the sensor back in to get the service mileage countdown to go higher than 2,500 miles?

BT cable. You can set the value to anything you want (it's actually a percentage value that translates to miles)

[VCP]

I know autologic scan tool can disable the brake pad light warning all together by coding. It also has a coding option for sport brake retrofit i guess bbl kit? going to ask tech support about that soon