How to Diagnose a Bad Starter on a Motor

Written by jody l. campbell
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Drivers often assume when their car does not start that the battery is the culprit. While this may be true on occasion, other components are involved with starting a motor that can also contribute to the failure, including a bad starter. Learning how to diagnose a bad starter can ensure you do not incur damage to the starter by misdiagnosing the reason for the engine failure.

Skill level:

Things you need

  • Voltmeter
  • Battery charger
  • Small hammer

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    How to Diagnose a Bad Starter on a Motor

  1. 1

    Listen. If you hear a distinct clicking sound when engaging the ignition, the problem is most likely not the starter. That sound indicates a weak battery that cannot produce enough cold cranking amps to engage the starter and turn the engine over. Boost the battery with a battery charger or check the voltage output with a voltmeter.

  2. 2

    Turn the lights on. Put the key in the vehicle in the on position and turn on the lights to determine if the battery connections are secure. If the lights dim or go out, you may have a bad connection to the battery. Check the cables for tightness and cleanliness. Corrosion can significantly decrease the output of the battery amps to the starter. If the headlights remain on and strong, then voltage is not reaching the starter, and other components may be suspect, such as the park/neutral switch or a bad ignition circuit switch.

  3. 3

    Tap on the side of the starter with a small hammer. Tapping helps to loosen the internal brushes inside the starter to turn in the event they are worn or seized in a certain position. If this works, you have a bad starter and should replace it quickly, because this method to start your engine will not continue to work for very long. Also, other functions of the starter may be at fault such as worn or broken teeth of the flywheel, which you cannot see without removing the starter.

  4. 4

    Check ground wires for the battery and the starter. Check wire connections to the starter and check the alternator and ground strap to the engine block. Replace or repair any faulty ground wires.

Tips and warnings

  • Do not continuously engage the ignition if the car will not turn over. Starters get extremely hot in a very short period of time. If the vehicle is cranking but does not turn over in about 30 seconds, allow the starter to cool (3-4 minutes) before attempting to start it again.

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