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3562RE: [bmw e28] ABS sensors

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  • Doug Dykaar
    Apr 29, 2005
      The abs sensors go bad because the cans rust inside the mounts. This can
      force the sensor element away from the rotating hub "gear" and reduce the
      signal strength. That's assuming the rust, squeezing on the sensor coil,
      doesn't cause an outright failure. I ruined one front just getting the thing
      out. The metal can tends to stay in the hole, when you pull out the sensor.
      I had a couple used ones on hand before I tried it.

      You can disconnect the ABS computer and use the plug with a voltmeter to
      measure the signal strength at a known speed. You can use an ohmeter to ID
      the pins from the sensor to the plug if you don't have a diagram.

      I have a fancy DVM that reads max signal, so I drove slow and read the value
      later. I also had the local Panzer mechanic use the Bosch diagnostic box. It
      can report the voltages for all four wheels. I believe the road speed is 30
      mph, but the important point is to identify the weak sensor(s).

      A symptom of a failing sensor is the abs coming on just before stopping,
      i.e. at very slow speed. The signal drops so low that the computer
      misinterprets it as lockup and the abs comes on. Not dangerous at <<5 mph,
      just annoying and you can bet it won't get better.

      Regards,

      Doug

      86 951 http://www.pcaucr.org/pcaucr/forum/post.jsp?postid=2393
      85 e28 535
      94 855 turbo wagon