How to Check a Starter Solenoid
When a vehicle's starter solenoid fails, a variety of problems can result--most notably the engine does not crank or is slow in cranking. Other problems include failure of the starter motor to disengage from the engine or a starter motor that continues to run when the key is no longer in the "start" position. A series of tests can help you check if the starter solenoid is bad and needs replacement.
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Instructions
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Attach the red clip of the voltmeter to the solenoid-side terminal of the wire that runs between the battery and the solenoid. Attach the black clip of the voltmeter to the solenoid lug where the battery wire attaches.
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Crank the engine and note how many volts the reading on the voltmeter drops by.
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Perform the same test on the connection to the opposite lug where the wire leads to the starter.
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Tighten the connection and repeat the test if there is a voltage drop of more than 0.3 volts. If the connections are good after that, test the resistance of the solenoid disc.
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Attach the red clip of the voltmeter directly to the solenoid lug where the battery cable attaches. Attach the black clip of the voltmeter to the opposite lug (where the cable leading to the starter is attached).
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Crank the engine again and note the voltage drop on the voltmeter. If the voltage drop is greater than 0.3 volts, then the solenoid disc is probably pitted or corroded, and the solenoid should be replaced.
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Tips & Warnings
Make sure the key is turned to "start" when you check the voltage drop, because the voltmeter will not give a reading without current flowing. If the wiring seems good but the starter doesn't engage when the key is turned to "start," it's possible that the internal coils of the starter solenoid may be faulty, for which there is only one remedy--to replace the solenoid.
Always wear eye protection when working in proximity to operating engine parts.
