How to Jump a Starter With a Bad Solenoid

You jump in your car, twist the ignition key and nothing happens. That unexpected silence may indicate the failure of your solenoid, one of the primary starting system components. The solenoid is an electromagnetic switch that causes the starter to engage the engine.

Isolating the problem

• 1

  To test for a bad solenoid, check battery voltage by placing a voltmeter across the terminals. A reading below 12 volts means a discharged or dead battery. If it is not a service-free battery, check the fluid levels and add distilled water where needed. Charge battery and recheck voltage. A reading below 11.8 indicates a dead battery.

• 2

  Examine the battery cables and terminal posts for corrosion or lose connections. Sometimes the cables have corroded under their protective covering, causing resistance and a drop in voltage. Use the wrench to loosen terminal nuts and remove the cables. Clean the battery posts with wire brush and reattach. Replace damaged cables.

• 3

  Use pliers to pull off the ignition lead at the solenoid. That wire and a thinner lead can be found on a separate terminal from the heavy battery cable terminal on the back of the solenoid . Attach the red lead from the voltmeter to the end of the ignition wire and ground the black lead to the starter frame. With the car in park, have a friend turn the ignition key to start. The voltmeter should read 12 volts.

• 4

  Remember, even if the starter is defective, the solenoid should still make a clunking noise when the ignition is engaged, assuming it is receiving the proper voltage. Because we have now verified sufficient power to the solenoid, and cannot hear the clunk of the solenoid plunger activating its lever when the ignition is turned on, the solenoid is definitely defective.

• 5

  To cause the starter's Bendix gear to engage the engine flywheel and crank the motor, the solenoid must function to power a lift lever that drives the starter drive gear into contact with the engine flywheel teeth. Jumping the starter will only cause the starter motor to freewheel without starting the engine.