The starter converts electrical energy into mechanical energy that engages and spins a gear on the rear of the engine. This gets the engine spinning so that it will start.


When a key is inserted into the ignition switch (1) and turned, voltage from the battery (2) is sent to the starter solenoid (3) to engage the starter (4).

The starter motor is mounted to the back of the engine block. When the key is turned to start the car or truck, the starter motor turns, engages with the flywheel by the starter solenoid and cranks the engine. When the engine starts and the key is released, the starter disengages the flywheel and stops turning so that the starter is not damaged by staying engaged with a turning flywheel.

Note: The ignition switch, battery, starter solenoid and starter all need to be in working order for the starter to engage properly. AutoZone can test your starter or alternator for free.
*Service not available in California


Oil/Fluid Soaked: Signs of oil, grease or corrosion are signs of a leak in the vehicle. These fluids can ruin intricate components and start engine fires. Leaks must be fixed before the starter is replaced.

Loose Mounting: Whenever a starter motor is being problematic because of excessive noise, visually inspect the mounting holes. If the mounting holes are out-of-round, it may have been caused by improper mounting.

Over Tightening: Do not use impact wrenches or breaker bars when installing a starter. It is important to hand-tighten mounting bolts before applying torque. Always alternate from one bolt to the other to avoid cracking the mounting flange. The mounting flange on a starter is made of cast steel.

Broken Gear: When you see a pinion gear with severely damaged teeth all the way around, it is typically from improper contact with the starter ring gear. This is usually caused by a faulty ignition switch. It can also be caused by attempting to crank the engine when it is already running.

Kick Back: This is caused by the engine rocking back while the pinion is engaged and the starter is trying to crank, but the pinion is misaligned with the flywheel. This can later damage the starter motor. The misalignment is usually caused by an existing fuel or ignition timing problem. This can also cause severe damage to the nose cone and/or the starter driver assembly.

Poor Grounding: The mounting bases are a key part of the starter motor's ground. These bases provide the electrical ground path to the starter. There should be a shiny metal-to-metal contact between the starter mounting base and the transmission or engine as well as between the nose cone and block.

Loose Electrical Connection: When the electrical connection to the starter motor from the battery is not tight, it can cause arcing and burning.

Melted Terminal: Cranking an engine for longer than 10-12 seconds causes critical electrical connections to become overheated and can cause them to melt.


Moisture: When moisture is inside of a starter solenoid, corrosion can occur that will interfere with electrical conductivity.

Overheating: Holding the ignition key in the 'start' position for an excessive amount of time pulls a lot of current through the starter solenoid and can melt contacts and solders.

Over Tightening: Excessive torqueing of fasteners can break posts or other vital components on or inside the solenoid.

Incorrect Wiring: Installing the solenoid incorrectly can cause the solenoid to short out and burn up internal components.


The starter solenoid acts as a relay, and in newer applications it extends the starter pinion. When starting a car, the battery sends electricity to the starter solenoid, but the solenoid will not send electricity to the starter until it receives a signal from the ignition switch when you turn the key. In older applications a bendix will extend the starter pinion.

When voltage from the battery is sent to the solenoid, a switch closes inside the solenoid and sends current to the starter. The starter then engages a gear that spins the flywheel or flex plate ring gear.

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