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Thread: ABS/BRAKE/DCS Lights on; Speedometer not working

  1. #1
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    ABS/BRAKE/DCS Lights on; Speedometer not working

    For the past couple weeks, my ABS, BRAKE, and DSC lights show up intermittently. It only happens once in every 3-4 trips. Sometimes, this happens during a trip. The car runs fine otherwise. The local dealership says I will have to replace my entire DSC unit for $2500ish. They also said my engine is misfiring in all directions and they'll have to do a smoke test. When I searched online and on this forum, its seems to me that its more likely caused by a faulty sensor. I plan to drive to Boston (from SC) in a few days and would like to fix it before I leave.

    Any advice/suggestions would be highly appreciated.

    Thanks.

  2. #2
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    Sounds like the dealer is trying to rip you off. They really diagnosed it as a faulty DSC unit?

    You need a new wheel speed sensor. Exactly which one would have to be determined by diagnostic software. If you're mechanically inclined you can try to rotating the sensors till you figure out which one it is. Rotate the drivers side sensors. If the speedo starts working then you know it is one of the drivers side sensors. This only works if one of the sensors is bad.

    Another common issue with these sensors is the magnets build up with road crud. Cleaning them off can make the sensor start working again.



  3. #3
    97heath528i's Avatar
    97heath528i is offline Eager to learn/wrench BMW CCA Member
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    Speedo is controlled by one of the rear sensors I believe. I would start there. Look for the wires to be exposed or contact with the pins is gone. Use OEM sensors for these as well.

  4. #4
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    Yes, I agree sound likes a wheel speed sensor to me. I am not sure which one but either right rear or left front.
    BTW, get BMW or OEM not aftermarket crap.

  5. #5
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    A couple of weeks ago I had a similar problem. My ASC, and ABS lights came on and I lost my odometer, speedo, cruise control, mpg gauge and the gas gauge acted funny.

    Turned out to be my drivers side rear speed sensor, the wires had frayed and I'm guessing the senor got shorted out because it failed while I was driving in the rain.

  6. #6
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    I've heard that it is the rear sensors as well, but that doesn't make sense to me. Why would a rear wheel drive car use a rear sensor (drive wheel) as a speed sensor. That mean that if the wheel slips the speedo would read some really high. Using a front wheel (non drive wheel) makes more sense.



  7. #7
    97heath528i's Avatar
    97heath528i is offline Eager to learn/wrench BMW CCA Member
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    I am not 100% positive on this. My tranny is controlled by the front sensor. I just recently fixed that issue. I am just saying that I would start with the rears and work forward. It will not take that much time. Report back and let us know what you find.

  8. #8
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    Thanks for the suggestions. I will get on it and keep you posted.

  9. #9
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    Quote Originally Posted by vsrinee View Post
    Thanks for the suggestions. I will get on it and keep you posted.
    If you are in a hurry to get it done rather than you do it yourself check with Inshore Imports at 901 inlet square dr in Murrells Inlet, TP# 843-651-1157. They have a good BMW indi mechanic and are cheaper than the local BMW/Mercedes Dealership Service Dpmt.

  10. #10
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    it's your lh rear wheel speed sensor wire harness.i'll bet the wire insulator is coming apart and showing the conductors.....

  11. #11
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    Quote Originally Posted by Xeniczone View Post
    I've heard that it is the rear sensors as well, but that doesn't make sense to me. Why would a rear wheel drive car use a rear sensor (drive wheel) as a speed sensor. That mean that if the wheel slips the speedo would read some really high. Using a front wheel (non drive wheel) makes more sense.
    have you ever been on a dyno?

  12. #12
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    +1 on the driver side wheel abs sensor. Same issue i had 6 months ago and took a peak...what do you know, a ripped wire at the sensor side. replaced it and no problem since.

  13. #13
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    Follow up:

    So, I took the car to a mechanic locally and he did find a faulty rear left speed sensor. But the same lights came up with the non-working speedometer on my way back home from the shop. Took it back next day, he said, there's a fuel trim code and that he fixed the vacuum hose trim and now it should OK.

    Now, as I was driving to Boston the next day (from SC), about half way through, somewhere near Philly, the same things come up again (ABS, DSC, Brakelights and speedo). I also see the fuel gauge is acting weird, mileage indicator is not functioning. Cruise is working fine however. I also noticed another problem now. If I drive speeds greater than 65 mph on the highways AND if I steer toward the left (even slightly; like changing lanes), the car shakes real bad. Steering toward the right is fine. And, this only happens when ALL the lights (and speedo not working) come up.

    Any insight would be appreciated.

    I'm in Boston, and fortunately haven't been driving much. But I plan to take the car to a mechanic this week. Anybody recommend a reliable indi mechanic in the boston area?

    Thanks.

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