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Thread: Brake lining warning and light

  1. #1
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    Brake lining warning and light

    I've replaced worn sensors before and have successfully reset the warning, but not this time.
    A few months ago I pulled my wheels just to inspect them. Pads were fine, sensors not touching, but noticed the wire on the front was a bit frayed but put it all back together and was fine. Weeks later i got the light and brake lining warning. I remembered the frayed wire. I pulled off the sensor, made a new splice, reset the warning and all was fine. For a few weeks. Now the brake lining warning and brake light are on. I bought a new sensor and have tried it on the front and back but can't get the warning to go away. I even tried just jumping the connector to bypass needing a sensor.
    What's going on?

  2. #2
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    Did you buy oem sensor ? Many people have bought aftermarket without much luck...every time I've replaced mine the light reset itself and the warning also
    Last edited by setconstr; 02-16-2019 at 05:26 PM.

  3. #3
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    I got a $10 ebay sensor that has worked before. But then forgot I could have just pulled an OEM off the parts car I have. That did not work either.

  4. #4
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    Another problem is that I believe there is a front and back sensor but it might just be the length of the wire it's definitely a different part number on my 01 sport

  5. #5
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    They are different connectors. you can't use the wrong one. not sure why that is though. these sensors just complete a circuit. some people cut them off and twist the two ends together.

  6. #6
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    Quote Originally Posted by RIboater2 View Post
    They are different connectors. you can't use the wrong one. not sure why that is though. these sensors just complete a circuit. some people cut them off and twist the two ends together.
    And both sensors are on the same loop. You've got an open line somewhere. Might have to get creative with a multi-meter if the sensors show a good loop.

  7. #7
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    still battling this. If i trace them back, where do the the front and rear wires finally come together? cutting the wires at each wheel and twisting together did not do it. Is there a single fuse just for this that I could remove to turn it off?

  8. #8
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    Quote Originally Posted by RIboater2 View Post
    some people cut them off and twist the two ends together.
    Please don't do that! Yes, I know some folks do exactly that, but that is also usually because it can feel darn near impossible to lookup the correct part numbers for the sockets used on the car side of the brake pad sensor circuit. I wrote a DIY for the E36 on this subject a few years back; at some point I will do one for my E38.

  9. #9
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    Quote Originally Posted by Thresher View Post
    Please don't do that! Yes, I know some folks do exactly that, but that is also usually because it can feel darn near impossible to lookup the correct part numbers for the sockets used on the car side of the brake pad sensor circuit. I wrote a DIY for the E36 on this subject a few years back; at some point I will do one for my E38.
    I just want the brake light to go out! My sensors are not tripped. Not ready for new pads.

  10. #10
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    Quote Originally Posted by RIboater2 View Post
    I just want the brake light to go out! My sensors are not tripped. Not ready for new pads.
    PUT the key in position 2 and have the door open wait 30 seconds the light will reset it self. I did it 2 minutes ago, Please try it
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  11. #11
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    Quote Originally Posted by franco90 View Post
    PUT the key in position 2 and have the door open wait 30 seconds the light will reset it self. I did it 2 minutes ago, Please try it
    Thank you but didn't work

  12. #12
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    How about the instructions below from the BMW TIS? Ignition position 1 (KL R) and ignition position 2 (KL 15) can be tricky and throw off a lot of "reset" attempts.


    Last edited by Qsilver7; 09-14-2019 at 03:44 PM.
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  13. #13
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    Quote Originally Posted by Qsilver7 View Post
    How about the instructions below from the BMW TIS? Ignition position 1 (KL R) and ignition position 2 (KL 15) can be tricky and throw off a lot of "reset" attempts.


    Thanks Q, expect no work was done. Brake light just came on one day. Sensors aren't tripped. So I made sure fluid was full and tried key position 1 for 30 seconds anyway. Light still on
    Originally, one day the brake light came on and just days before I had been changing a tire and checked that sensor as the wire looked a bit frayed. So I unplugged it and plugged it back in and was able to reset the light. Easy fix. Then weeks later the light came on again and no fiddling with the sensor plug would work this time so I got a new sensor and still didn't work.

  14. #14
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    RI...what color is the brake light warning....red or yellow? The color makes a difference. I'd have to check the owners manual for the specifics between the two.
    Become a BMW CCA member! Click HERE to join and feel free to use my BMW CCA member #191509 as a referral.

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  15. #15
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    I was going to ask the same thing. Wonder if you are, coincidentally, dealing with two different issues.

  16. #16
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    ​red

  17. #17
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    mine is RED AS WELL
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  18. #18
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    Just for kicks, check that the wire is plugged into the brake fluid level sensor and check that the brake fluid is topped off.

    I thought these brake wear sensors worked by shorting the two wires to ground when the sensor wears down and makes contact with the rotor? So make sure nothing is shorted to ground?
    Last edited by racer2086; 09-16-2019 at 09:03 AM.
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  19. #19
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    There is a resistor in the sensor, you can't just splice them together. It is about 470ohms if memory serves me. If you spliced the wires I would think it would be fine but lord only knows how picky the software is?
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  20. #20
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    I think if you splice it together wouldn't it throw the light? My worn sensors have had a copper contact that gets exposed when the pad wears down enough to let the rotor wear through the plastic exposing the copper contact to the rotor. I imagine splicing the wires together cause 0 ohms, just like if the sensor was making contact with the rotor?
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  21. #21
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    Quote Originally Posted by racer2086 View Post
    I think if you splice it together wouldn't it throw the light? My worn sensors have had a copper contact that gets exposed when the pad wears down enough to let the rotor wear through the plastic exposing the copper contact to the rotor. I imagine splicing the wires together cause 0 ohms, just like if the sensor was making contact with the rotor?
    I thought it was the opposite. That the sensors completed the circuit with a thin wire embedded in it and when the plastic wore down it broke through the thin wire connection.
    you're saying the sensor completes the circuit when coming in contact with the metal rotor?

  22. #22
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    The plastic definitely wears down and exposes a metal contact that touches the rotor. I think at that point it completes a circuit to ground.

    I just looked it up in newtis.
    https://www.newtis.info/tisv2/a/en/e...mation/nIUiEoG

    The front and rear brake sensors are wired in series to the IKE. When healthy, they complete a circuit from the IKE back to the IKE. When 1 sensor wears through, it breaks the circuit to ground, thus triggering the light. If both sensors are worn and shorted to ground via the rotor, replacing one will not get rid of the light since the other is still shorted to ground. This also explains why people would twist the wires together. That is simply completing the circuit and skipping the sensor.

    You need to check both sensors to be sure they're healthy and not worn through and also check your brake fluid level and the plug going to the sensor as that can cause the brake light. Of course if the fluid level is low the cluster should also give you a text warning of brake fluid low.
    Last edited by racer2086; 09-17-2019 at 10:37 PM.
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 270k
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    mods: m-pars | Bilsteins & B&G springs | ValentineOne | StealthOne
    retrofits: full nav | MKIV | bluetooth TCU | BM53 w/ AUX input | video module w/ AV input & backup cam | oem sirius xm | xenon | shades | PDC | rain sensor | BMW DWS TPMS | lighted door handles | front seat heaters | heated steering wheel | euro rear fog lights | ski pass | folding mirrors


  23. #23
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    The resistor would be to limit the current through the circuit. It may not matter but with BMW?
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    00' 740il Dinan, CAI, Romulus exhaust, Stage 5 engine and transmission tune, 750 brakes, camber plates, strut tower brace. Sold
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    03' 525i wagon for the wife, sold
    98' 740i for the daughter, wrecked
    92' 525i with over 200k, wrecked
    02' R1200 CLC, hit by a bus and broken in half. That one made the news!
    It's like herpes there is no cure but if treated properly you can live with it for the rest of your life

  24. #24
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    Fluid is full and I pulled the connector off/on to check it.
    If wearing down the plastic tabs completes a circuit, (I always thought it broke a circuit) then removing these sensors all together means the circuit will always be open and the light should go out?

    Is there a way to just disable this system? I don't really need a light to tell me it's time for pads anyway. If it were just one fuse I'd pull it.

  25. #25
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    Ok, lets make sure we're all on the same page with a few things...

    First, the sensor sticks into the pad with a metal clip. That clip has nothing to do with the sensor. The face of the sensor that faces the rotor, however, has a little plastic ridge, directly under which is a strip of metal. See pic.



    As the pads wear down, that ridge on the sensor starts to contact the rotor, which wears through the plastic making contact with the metal beneath. This is the grounding of the sensor I was referring to.

    So, the IKE is expecting a certain amount of current through the closed circuit with two healthy sensors in series. There may be some resistance to those sensors, which is easy to test by putting an ohm meter to the sensor leads out of the car.

    When one of the sensors contacts the rotor, that circuit on the diagram doesn't make it back to the IKE and instead heads to ground at one of the two sensors, so the closed circuit in the diagram to the IKE is lost, which tells the microprocessor to trigger the brake light.

    I do not know for certain what leaving the sensor out would do because I've never tried it. I would imagine that leaving the sensors out would still trigger the IKE, because the circuit wasn't being completed at all due to the open circuit of the sensor missing. Whatever brain in the IKE is expecting a certain current through that circuit, but if a sensor is missing or worn through, it's not going to see that and will trigger the light.

    Hope that makes sense. So if the sensors are both good, connected, and not worn through and not contacting the rotor, you may have a wiring harness problem of a broken wire or shorted wire (more than likely right near the plug underneath the plastic wheel shroud.

    Could you be a little more specific with the frayed wires you reference in OP and how you repaired it?
    Last edited by racer2086; 09-18-2019 at 03:34 PM.
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 270k
    '04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 120k
    '00 540i sport | Titanium silver | Black | 5AT | 152k
    '85 Mustang GT convertible | Medium charcoal metallic | Gray | 5MT | 216k | one owner, all original

    mods: m-pars | Bilsteins & B&G springs | ValentineOne | StealthOne
    retrofits: full nav | MKIV | bluetooth TCU | BM53 w/ AUX input | video module w/ AV input & backup cam | oem sirius xm | xenon | shades | PDC | rain sensor | BMW DWS TPMS | lighted door handles | front seat heaters | heated steering wheel | euro rear fog lights | ski pass | folding mirrors


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