How to Diagnose a Car Starter's Solenoid System

Failure of an engine to crank when the key is turned to start may be due to a defective starter solenoid. If no movement of the solenoid plunger can be detected, follow the specific procedure outlined in the vehicles service manual to safely remove the starter and use the following steps to "bench test" the starter solenoid.

Difficulty: Moderately Challenging

Instructions

Things You'll Need:

• open end box end wrench
• Ratchet set (optional)
• Volt meter
• Ohm meter (or combination of two functions)

Bench testing a starter solenoid

1. Disconnect starter from battery and disconnect battery cables. A starter solenoid has two windings. Each winding must be checked separately. This is most easily done with the starter on the bench. Disconnect the heavy connector between the solenoid and the starter. Connect one ohmmeter lead to the switch (S) terminal. Connect the other lead to the terminal that was connected to the starter.

2. Next connect the ohmmeter leads from the (S) terminal to the solenoid case. If the ohmmeter reading from either lead indicates an open circuit, replace the solenoid. If the solenoid plunger does move, but the cranking is slow, the problem may be high resistance in the main cranking circuit. Use volt meter to measure voltage drop to determine if high resistance is present. The voltage drop across the solenoid contacts is higher than specified, (0.3 volts), the solenoid must be replaced.

3. Replace the solenoid per the specific year model service manual and reinstall starter. Ensure battery cables remain disconnected to protect against electrical shock.

4. After starter is installed, reconnect wire leads to starter solenoid and starter if disconnected. Reconnect battery cables and check battery voltage (should be 12.5 - 14.0 volts). If battery voltage is low, charge battery before checking solenoid function. Make sure the vehicle is in the park position or clutch is engaged and crank the engine. Listen for grinding noise as starter is turning (stop if noise is heard). If noise is heard, check starter installation and ensure proper number of shims are in place. Engine should crank smoothly without grinding indicating that the solenoid is properly installed and functioning as designed.

Tips & Warnings

• Safety glasses should be worn throughout the procedure. Gloves should be worn when handling batter cables. Care should be taken when removing the starter to avoid accidentally crossing both battery terminals. Failure to do so can cause electrical shock and damages circuits.
• If battery is bulged or heavily corroded, battery should be replaced before working on starter.
• Failure to stop cranking the engine when grinding is heard, could cause damage to engine flywheel.