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Common Symptoms of a Faulty Starter Motor

By R&D
Published on May 19th, 2025

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The starter motor is an essential component of a vehicle's starting system. It is typically located near the engine's flywheel. Its primary purpose is to crank the engine by converting electrical energy from the battery into mechanical energy, initiating the combustion process needed to start the vehicle.

Common Symptoms of a Faulty Starter Motor

The starter motor includes the armature, solenoid, commutator plates, brushes, and drive gear. When the ignition key is turned, the solenoid engages, allowing electrical current to flow through the commutator plates and brushes, creating an electromagnetic field in the armature. This field interacts with the stator’s magnetic field, causing the armature to spin rapidly with high torque. The resulting motion turns the drive gear, which engages with the engine's flywheel to crank the engine. Once the engine starts and the key is released, the solenoid disengages, retracting the drive gear from the flywheel, and the starter motor stops.

A faulty starter motor can lead to a range of issues, such as the engine failing to crank, slow or intermittent starting, or unusual grinding noises. These problems can leave the vehicle inoperable, causing inconvenience and potential safety risks, making timely diagnosis and repair crucial.

This article highlights the typical symptoms of a faulty starter motor, to help you identify potential issues and their root causes.

What Causes Starter Motor Failures?

Worn-Out Brushes or Commutator: Continuous use of the starter motor leads to wear on brushes and commutator plates. Brushes that are excessively worn fail to make adequate contact with the commutator, reducing the flow of electrical current. This poor contact increases resistance, causing the starter motor to operate intermittently or not at all. A damaged commutator may also hinder starter motor performance and lead to eventual failure.

Loose or Corroded Electrical Connections: Loose or corroded electrical connections at battery terminals, the solenoid, or ground points can disrupt power flow to the starter motor. Corrosion buildup increases electrical resistance, making it difficult for current to reach the motor. Vibrations from the engine may also loosen connections over time, causing intermittent operation or a complete loss of function.

Faulty Internal Windings: Internal windings in the starter motor can be affected by shorts, open circuits, or overheating. These faults reduce the starter motor's torque output and efficiency. Damaged windings can also lead to excessive electrical resistance, causing the motor to struggle or fail to crank the engine altogether.

Damaged Drive Gear or Overrunning Clutch: The drive gear is responsible for engaging the flywheel to crank the engine. Worn or broken teeth on the drive gear prevent proper engagement, resulting in grinding noises or failure to turn the engine over. Additionally, a malfunctioning overrunning clutch can cause the gear to spin freely without transferring torque, preventing the starter motor from starting the engine.

Oil Leaks and Contamination: Oil leaks from nearby engine components can seep into the starter motor through a damaged seal, contaminating its internal parts. Oil inside the starter motor can cause electrical shorts, increase mechanical friction, and accelerate wear on the brushes and gears. Contaminated components may bind or deteriorate, ultimately preventing the starter motor from functioning properly and reducing its lifespan.

Common Symptoms of the Faulty Starter Motor

Dashboard Lights Turn on, but the Engine Fails to Crank

When turning the ignition key or pressing the start button, if the dashboard lights come on but the engine fails to crank, it can be a sign of a faulty starter motor. This indicates that the battery is supplying power to the vehicle’s electrical systems, but the starter motor is unable to engage or function properly. This issue could be caused by worn-out brushes, faulty solenoids, or a damaged drive gear.

Intermittent Starting Issues

A failing starter motor may cause inconsistent or delayed starting. The engine might crank in some cases, while at other times, it doesn’t respond. This inconsistency is usually caused by worn brushes, a failing solenoid, or loose connections, which prevent the starter motor from functioning reliably.

Grinding Noise During Starting

If there are worn gears or a faulty drive mechanism, the starter motor may produce a grinding noise when attempting to start the engine. This occurs when the drive gear fails to mesh properly with the flywheel. Persistent grinding can lead to damage to both the flywheel and the starter motor, worsening the issue over time.

Smoke from the Starter Motor

If the starter motor is overworked or suffers from electrical issues, it can overheat and produce smoke. This symptom typically indicates internal damage, such as shorted windings, a stuck solenoid, or excessive friction within the motor. The smell of burning electrical components may accompany the smoke, signaling immediate attention is needed.

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Identify a Faulty Starter Motor with the Innova Scan Tool

The Innova Scan Tool quickly retrieves and identifies existing Diagnostic Trouble Codes (DTCs) stored in your vehicle’s computers. With a quick OBD2 Scan, you can retrieve existing DTCs, the I/M Status of the vehicle, and any collected Freeze Frame data from these computers. Refer to the Innova Coverage Checker to determine the level of information supported on your vehicle by year, make and model. The Innova Scan tool effectively diagnoses starter motor-related issues, helping you easily pinpoint and resolve problems.

The Innova Scan Tool offers the ability to view Live Data PIDs and displays OEM-Enhanced Live Data, providing advanced insights for comprehensive vehicle diagnostics. It also lets you monitor the Starter Signal, enabling you to assess the starter motor's real-time status for more accurate troubleshooting. The optimal operating values for the starter motor may vary depending on the specific make and model of your vehicle.