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ABS Troubleshoot Question

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  • ABS Troubleshoot Question

    Hi all,
    Lots of talk on Hubs and ABS lately,. I will throw in my scenario.

    Having trouble with my ABS on my 89 189,000 miles.

    Front brakes.
    Changed ABS speed sensors on both sides of the front wheels. Now front left ABS starts activating just prior to coming to a full stop.
    Didnít happen before. (Not sure if left side was not functioning). Very embarrassing pulling up to a light and it sounds like your
    brakes have gravel in it. I changed the sensors because the insulation on the harnesses were starting to disintegrate. (Memphis Car).

    Thinking that the ABS rings were broken or dirty I clean them and inspected them while they were still attached to the hubs.
    (Compressed air, light scraping and a stiff toothbrush). No rust on the teeth and also doesnít look like there are any
    broken/chipped ones either. I cleaned both sides. Reconnected all harnesses and still the same problem.
    I disconnected both harnesses to disable the front abs sensors. No problems stopping - No noise.

    So what could be wrong? I can drive without the ABS but would surely like to know what the reason behind this is. .
    Both new sensors were tested and resistance was within the factory specs.

    Anyone have any idea what is going on here? The Activated ABS at low speeds is on dry pavement so there is no authentic reason for the activation of the ABS.

    Also I did not see any ABS light come on even when I start up the car.

    CanuckM3

  • #2
    This is a silly question but what are your wheel specs and tire sizes? The ABS rings will run a completely different rotation if your on a big staggered set up with different overall diameters. Thus leaving you with a different rotation Front vs Rear and a confused ABS system
    sigpic 95 M3 & 88 M3

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    • #3
      Not a silly question. Car is 100% stock. Stock 15 inch basket weaves and OEM size tires

      canuckm3

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      • #4
        Whenever I have a problem that was introduced by something new I've installed, I back that change out and reinstall the old part(s), and the vast majority of the time (like almost always), the problem goes away. In your case, it's very easy to swap the old parts back in assuming you still have them. I'd swap them one at a time and test in between because my bet is you have one bad sensor even though they ohm out properly.
        Ron ///Man

        • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
        • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
        • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
        • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
        • '89 M3 M3T / ITR Club Racer
        • '94 Spec E36 - Eh....
        • '09 M3 - Tarmac Terrorist
        • '04 330Xi Sport 6 Speed - Snowmobile
        • '07 530 Xi - Highway Star
        • http://www.imwcarparts.com/e30-m3-parts.htm


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        • #5
          Originally posted by Ron ///Man View Post
          Whenever I have a problem that was introduced by something new I've installed, I back that change out and reinstall the old part(s), and the vast majority of the time (like almost always), the problem goes away. In your case, it's very easy to swap the old parts back in assuming you still have them. I'd swap them one at a time and test in between because my bet is you have one bad sensor even though they ohm out properly.
          Thanks, I will see if I have that part still intact. As I remember the plug may have disintegrated. I am sure I can retest..
          Although the right side and left side sensor's Part Number is different, it looks 100% interchangeable. Anyone know if they are?

          CanuckM3

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          • #6
            if the chassi plug has disintegrated possibly you could have the terminals in the wrong way around and the computer sees one wheel going backwards?

            E30 M3 1987
            Mini Clubman GT
            BMW E36 323 Msport
            Toyota Corona
            KTM 200EXC
            Honda CB50 (1979)

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            • #7
              Originally posted by CanuckM3 View Post

              Thanks, I will see if I have that part still intact. As I remember the plug may have disintegrated. I am sure I can retest..
              Although the right side and left side sensor's Part Number is different, it looks 100% interchangeable. Anyone know if they are?

              CanuckM3
              Thanks for replying Dave.

              Yes. I did splice a new male side in on the chassis harness. I was very careful in the polarity but I could have overlooked
              it. I thought it wouldn't make a difference. Is there a way to test with a voltmeter? Ground one side and put the voltmeter
              on the other terminal? I could also run clips and reverse the plug and do a road test.

              CanuckM3

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              • #8
                Hi,
                I think you should do as Ron suggested install the original sensors try that first if that does not fix it reversing the wiring at the L/H abs plug in the may be the next option you have to be careful with that as I don't know what will happen when brakes applied if that was not the cause of the problem.

                When the wheel is spun one way it would be a + Volt square wave and when it is spun the other way it would be - Volt wave so that is what the ABS would see if one sensor was wired different than the other.





                E30 M3 1987
                Mini Clubman GT
                BMW E36 323 Msport
                Toyota Corona
                KTM 200EXC
                Honda CB50 (1979)

                Comment


                • #9
                  I've had the same problem and solved it by replacing one front speed sensor.
                  On the bosch abs 2 LED Tester that sensor generated a weaker signal than the others which meant that it dropped away at a slightly higher speed than the other three signals and thus tricked the abs into sensing a locked wheel as soon as I applied the brakes and came close to a standstill.

                  Your abs light should come on when starting the engine and switch off after a self-check and stay off. If it Turns on when you've reached a speed of 4mph (or so) then one of the speed sensors is faulty.

                  Best way to identify which sensor is faulty is disconnecting 3 of them, keep 1 connected and then start car and drive.
                  If the abs light stays off that's your faulty sensor. Explanation: When that sensor is faulty the abs gets a signal that is identical to a stationary car that has 4 working sensors I.e. no signal and the light stays off even when driving faster than 4mph. (As originally Posted by Mr Mcar on the SIG if memory serves me right)

                  To disconnect the rear sensor you only have to pull (yank) up the rear seat cushion and unplug the connectors.

                  The (front) Sensors are mirror images where they attach to the stub axle/hub but still fit and work

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