Starters fail for several reasons, one being the starter solenoid. The solenoid is a component of the starter - an electromagnet - that serves two purposes. When the magnet is energized, it pulls a sliding arm in that levers the starter drive gear out. The gear meshes with the flywheel ring gear. It also closes two contacts, allowing power to flow to the starter motor. Although integral to the starter, you can service or replace the solenoid as needed.
Raise the hood of the car and disconnect the negative battery cable. Depending on the model, if the starter is removed from under the car, jack up the front of the car and install jack stands under the frame, then lower the car onto the jack stands. Push against the car to make sure it is sitting firmly on the jack stands. If it rocks or wobbles, reset the stands.
Use a 3/8-inch socket wrench and remove the starter mounting bolts, followed by the positive battery cable and the small, solenoid control wires. Depending on the model, the small wire will unplug or be held in place by a retaining nut. If it is held in place by a nut, use a 1/4-inch socket to loosen the nut and remove the wire harness connector.
Test the solenoid with battery power. Mount the starter in a vise and clip a negative cable to the starter body. Starters ground through their body and do not have a separate ground, or negative, wire. Install a positive cable to the large, positive connection. When the solenoid is now energized, the starter will operate if it is functioning properly.
Apply positive battery voltage to the small solenoid connection that was unplugged or detached with a small socket. Use a small jumper wire and touch it to the connection. The starter drive-gear should quickly extend with some force as the magnet energizes, and the starter motor should spin as the solenoid closes the internal contacts that allow power to flow to the motor. Remove the small wire and the process stops.
Repeat the starter test and notice the solenoid operation. If the starter gear extends, but the motor fails to turn, the problem is with either the solenoid or the starter motor. To test for this, bypass the solenoid. Coming out of the motor is a bridge-connector that attaches the motor to the solenoid. Power flows from the contacts inside the solenoid, through this bridge-connector, into the motor. Apply power directly to this external bridge. If the motor is good, it will spin when positive voltage is applied. If it spins, the contacts inside the solenoid are defective.
Remove the solenoid from the starter motor. Remove the two mounting screws that attach the solenoid to the starter. Remove the lower bridge-connector screw. Once removed, twist the solenoid 90 degrees, left or right, to unseat the lower mounting flange. This is needed to keep the solenoid firmly mounted because of the forces involved when the solenoid levers out the drive-gear. Pull the solenoid off, and at the same time, remove the large, drive-gear return spring.
Install a new solenoid by placing the return spring in place, then locating the solenoid flange in place, then twisting the solenoid and lining up the screw holes. Reinstall the mounting screws and replace the lower bridge screw. Bench test the assembly before installing it on the car.
