[ManImCool]

I bought a 2006 330i a couple months ago, with no brake warning lights. The red warning service light recently came on with the brake signal saying to get them checked immediately. I know for a fact that the sensors or something is at fault because the brake pads are practically new. I was at a mechanic's the other day with another car on a non-related thing and I casually mentioned to him what I believed to be a faulty brakepad sensor. He told me he'd take a look, but strongly warned me NOT to reset the service computer (which I thought about doing with the Carly coding app). He also told me it's really easy and quick to fix faulty sensors and that I could probably manage doing it myself.

Assuming it is in fact the brake pad sensor(s), can someone guide me on how to make this brake light warning go away? Can I just do some simple coding or computer reset (and why would a mechanic care if I do this)? Or do I have to replace the brake pad sensor, and then and only then can I do the reset (or will the computer detect the new sensor and coding/resetting will not be necessary)? If I do have to replace the brake pad sensor, how do I tell which one to replace? Do/should I need to replace all of them?

Thank you!

[ManImCool]

gentle bump

Should this be in a different thread?

[titium]

on my 135 it has two systems one where it trys to estimate the pad life left (based on a variety of factors) then a second system which relies on the sensor.

if it is well and truly low pads or a dodgy sensor I'd expect the symbol to show up again after you reset it. if it's the first senario then the last guy to replace pads probably didn't reset it so it still thinks you have the old pads the calculated system also isn't accurate with pads other then oem.

[TheBingoBalls]

I don't see why he warned you not to reset the sensor. First, you said your pads are practically new so even if you did reset it, the counter would sort of coincide with remaining brake pad life. Worst case, if the pads had gone through half its life and you reset the sensor, the counter would reset to full pad life, which is inaccurate, but at the same time not a problem if you're not constantly checking brake pad life. Once the pad gets worn enough, it's going to trigger the sensor anyway.

Expanding on what titium said, if the previous owner never reset and the counter naturally triggered the warning, you should be able to reset the sensor. If not, then it might be a sensor issue where you just need to replace it. Had a similar issue with my aunt's X6. iDrive threw rear brake pad warning but pads had a lot of life left. Unplugged/plugged the sensor and reset the warning.

[PhaseP]

He said not to reset it, because if sensor tripped first stage, computer will give red brake light immediately upon reset attempt. Computer allows reset only with a sensor that hasn't reached first stage. OP can get a new sensor replace and reset, or short circuit the wires and reset, which is what new sensor looks to the computer, short circuit.
I posted about this a lot of times, with detail on how the sensor really works and etc.

It would be nice if a FAQ sticky thread was made for these common questions, like how two stage brake sensors and computer work together, or why speedometer 5% lower than my real speed, or where is that extra cable supposed to be connected that I found near the battery, or under the seat, or is it normal that I feel windshield wiper movement on the brake pedal and or I hear my engine ticking when is it going to explode or what engine oil should I use and so on

[VTECaddict]

If the sensor has made contact with the rotor and has ANY wear on it, the CBS will not let you reset the system and it will give you ---- and constant red brake warning if you try to reset it. This is why you should never reset the brake service unless you have brand new sensors in or modified it to bypass the sensor.

A worn sensor with new pads should not trip the red brake warning until the sensor wears down to the second stage. The mileage counter will just stop counting down or even go up until the new pads wear down enough for the sensor to contact the rotor again.

[PhaseP]

If the sensor has made contact with the rotor and has ANY wear on it, the CBS will not let you reset the system

For reset, it can have some wear on it, but not up to the point that sensor's resistance starts reading 470 ohms instead of short circuit, which is its first trip point. One can disconnect the sensor wire, measure its resistance. If it reads around 0.2 or 0.4 ohms (which is the resistance of the leads and contact points) it can be reset. If it reads 470 ohms it has tripped first stage, can't be reset. If it reads open circuit, i.e. a very high resistance value, pads are close to be done, needs replacement.

See this one for more detailed explanation:
http://www.e90post.com/forums/showthread.php?t=981050

[TheBingoBalls]

Originally Posted by PhaseP

For reset, it can have some wear on it, but not up to the point that sensor's resistance starts reading 470 ohms instead of short circuit, which is its first trip point. One can disconnect the sensor wire, measure its resistance. If it reads around 0.2 or 0.4 ohms (which is the resistance of the leads and contact points) it can be reset. If it reads 470 ohms it has tripped first stage, can't be reset. If it reads open circuit, i.e. a very high resistance value, pads are close to be done, needs replacement.

See this one for more detailed explanation:
http://www.e90post.com/forums/showthread.php?t=981050

This. Or at least thats how I think the sensor works. I had an issue with a X6. The pads had a ton of life left but the iDrive threw the warning. I unplugged the sensor and reconnected it and then reset it in iDrive and everything was fine. I'm not saying you're wrong in anyway, you could be 100% correct and it might be luck and purely a coincidence, but I've never had any issues with resetting a sensor that threw a fault when it wasn't even close to being worn or damaged. I always approached it as if the sensor has not touched the rotor, reuse and reset.

[SlimE92]

I heard that if u have a new sensor in and u reset the brake sensor that it'll short circuit it and renders it useless even if the sensor did not make contact, maybe that's why he said not to reset it since u got new brakes

[ManImCool]

Well, I tried to take the easy way out and reset the computer because all pads are pretty new. In the reset menu, I believe I got the rear brakes to reset, but no matter how many times I try to reset the fronts, the miles number only resets to some relatively low number (off the top of my head, I think I remember it being 5K? 7.5Kish?) And the brake/service light remain on.

Does this mean the front sensor needs replacing, and the back sensor is fine? Are there 2 sensors in the front (L/R) or just one, and if so, what side is it on? Is it possible an unplugging and replugging might fix this, or is it time to just order a new sensor?

[SlimE92]

Just one in the front and one in the back. Yea at this point I would pick up a new one. They're about 10 bucks on eBay

[ManImCool]

Left side? Right side? Are all E90 brake sensors are the same, or do I have to worry about buying a model specific or rear/front specific or left/right specific?

Thank you!

[SlimE92]

Originally Posted by ManImCool

Left side? Right side? Are all E90 brake sensors are the same, or do I have to worry about buying a model specific or rear/front specific or left/right specific?

Thank you!

Check out realoem.com for all part numbers relating to your car specifically, it's also a good way to know your car and how it works