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Proximity switch/sensor testing?

Discussion in 'Electronic Repair' started by Alistair Ross, Mar 16, 2005.

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  1. New to the group, so apologies if this question has been asked before.

    My car is fitted with a sensor that tells the ECU that manages the auto
    gearbox what RPM's the engine is running at.
    The error code on the car points to the sensor not sending the RPM's to the
    ECU
    Before I fork out £60 for another sensor is there a way of using digital
    multimeter to test it?
    The unit is a plastic moulding with two wires, and has quite a strong
    magnetic field.

    My level of expertise?....Novice!

    All help appreciated.......ttfn........Alistair
     
  2. Bob Shuman

    Bob Shuman Guest

    Sounds like a generic Hall Effect Vehicle Speed Sensor/Switch. I've never
    found away to test them, but the failure mode is no signal to the vehicle's
    computer, so the error code gets set. Depending on if it is the input
    (engine to trans shaft speed) or output (trans output to vehicle wheels)
    that failed some other nasty things can happen as well since these speed
    sensors are used to determine the automatic transmission's shift points and
    also sends the vehicle's speed to the speedometer.

    I have found that these fail fairly often. I have replaced 4 of them in
    several different makes and models of vehicle over the last 15 years. The
    last one was last year on a minivan that had about 40K miles. They are
    usually pretty cheap ($30) and easy to locate and replace. My only advice
    would be to make sure you have the correct one since in most vehicles there
    are two (input and output).

    Good luck.

    Bob
     
  3. Jerry G.

    Jerry G. Guest

    These sensors, are not able to be verified with an ohm meter. They are
    usually a Hall effect device. These also have different specs, depending on
    their designed application. The testing of one of these is fairly complex.

    You could run the motor, and see on a scope the output of it, but you would
    have to know the exact characterises in the waveform that you are supposed
    to have. This would be the amplitude, timebase, and its form. The dealers
    and service centres would have dedicated test facilities to test these
    devices, and to be able to test the computer unit as well.

    It is possible that the sensor, or the computer that is reading it may be
    defective, or it may be a simple wire or connector problem. The best test is
    to substitute the parts. This is why it may be cheaper to go to a service
    centre to have them check it for you. You will have to buy the parts to try
    them, and I don't think they are returnable.

    --

    Jerry G.
    =====

    New to the group, so apologies if this question has been asked before.

    My car is fitted with a sensor that tells the ECU that manages the auto
    gearbox what RPM's the engine is running at.
    The error code on the car points to the sensor not sending the RPM's to the
    ECU
    Before I fork out £60 for another sensor is there a way of using digital
    multimeter to test it?
    The unit is a plastic moulding with two wires, and has quite a strong
    magnetic field.

    My level of expertise?....Novice!

    All help appreciated.......ttfn........Alistair
     
  4. Thanks....ttfn........Alistair
     
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