What can cause a starter to fail?

Quick answers

The most common causes of starter failure are:

  • Worn starter gear teeth
  • Bad starter solenoid or relay
  • Weak battery
  • Faulty ignition switch
  • Dirty/corroded battery connections

When you go to start your car and hear nothing but a click or a grinding sound, you likely have a starter problem on your hands. The starter is responsible for spinning the engine fast enough to allow it to start when you turn the key or push the start button. If the starter can’t do its job, the engine won’t start.

There are several components that make up an automotive starter system. Knowing how these components work and interact with each other will help you better understand what can go wrong and cause the starter to fail. In this article we’ll take a closer look at the starter system, the most common causes of starter failure, and some troubleshooting tips to isolate the problem.

How does an automotive starter work?

The starter motor itself is essentially a powerful electric motor. When you turn the ignition key or push the start button, it engages the starter solenoid, which then pushes the starter drive gear forward so it meshes with the flywheel/flexplate. At the same time, it sends electricity from the battery to the starter motor, causing it to spin. As the starter spins, it turns the flywheel, which cranks the engine. Once the engine begins firing on its own, the starter disengages and comes to a stop.

There are a few key components that allow this process to happen:

  • Starter motor – The electric motor that provides the spinning force to turn over the engine.
  • Starter solenoid – The relay that engages the starter motor when electricity is applied. It pushes the drive gear out to mesh with the flywheel.
  • Starter drive gear – The small gear on the starter motor shaft that meshes with and turns the flywheel.
  • Flywheel/flexplate – The large gear attached to the engine’s crankshaft that the starter drive gear meshes with to spin the engine.
  • Battery – Provides electricity to power the starter motor.
  • Ignition switch – Sends power to the starter solenoid when the key is turned or start button is pushed.
  • Cables and connections – Provide electrical connections between components.

When any one of these components fails or has an issue, it can lead to problems with the starter and prevent your engine from cranking and starting. Next we’ll look at some of the most common issues.

Common starter failure causes

There are a variety of issues that can prevent a starter from working properly. Here are some of the most common causes of starter failure:

Worn starter gear teeth

The small drive gear that extends from the starter to mesh with the flywheel has teeth that can become worn down over time. After thousands of starts, the grinding action between the starter gear and flywheel gradually erodes the metal teeth. Excessive wear will allow the gear to slip on the flywheel rather than turning it. Replacement of the starter is needed when this happens.

Bad starter solenoid or relay

The solenoid is essentially the switch that energizes the starter motor when you attempt to start the car. It can fail in a couple ways. The contacts inside the solenoid can wear down or get stuck, preventing electrical current from reaching the starter motor. Or the solenoid may fail to fully engage and push the drive gear out to mesh with the flywheel. In either case, the starter won’t turn over the engine. If the starter solenoid fails, the entire starter will need to be replaced.

Weak battery

The battery is critical for providing the surge of power the starter needs for cranking the engine. A weak battery may still have enough charge to operate the lights and electronics, but not enough to engage the starter. Low voltage prevents the solenoid from fully closing and engaging the starter motor. A battery should be load tested to determine if it needs to be replaced.

Faulty ignition switch

The ignition switch signals the starter solenoid to operate when you turn the key. If the switch fails, becomes loose, or loses electrical contact, it can interrupt the signal to the solenoid. This will prevent starter operation. The ignition switch would need replacement in this case.

Dirty or corroded connections

Corrosion on the battery terminals or the main positive and negative starter cables can cause increased resistance. This may prevent sufficient electrical current from reaching the starter. Cleaning the connections is usually all that’s needed to resolve this issue.

Damaged flywheel teeth

While not extremely common, the flywheel ring gear can sometimes become damaged. If the teeth are excessively worn or some are missing, the starter will slip and fail to turn over the engine. This would require flywheel or flexplate replacement.

Starter drawing too much current

If something inside the starter motor has mechanically failed, it may begin to draw excess current. This places a heavy load on the battery and electrical system that can cause the starter to not work or suddenly stop cranking. An internal short, binding brushes, or rubbing armature can be causes. The starter will need to be inspected and tested or just replaced.

Engine seized

In very rare cases, the engine itself may have seized due to lack of oil, coolant leak, or thrown rod. When this happens the starter motor is unable to physically crank the engine. This usually requires major engine work or replacement.

Broken teeth on ring gear

If the ring gear on the flywheel has any broken or missing teeth, the starter will be unable to properly engage and turn the flywheel. Inspect the flywheel ring gear teeth carefully for any damage. If found, the flywheel or flexplate will need to be replaced.

Bendix drive stuck or frozen

The small drive pinion gear that pops out when the starter is engaged is called the Bendix drive. If it becomes stuck or frozen in place from dirt, debris or corrosion, it can prevent the starter drive gear from properly engaging the flywheel. The starter will need to be removed, disassembled and cleaned or just replaced.

Starter failure troubleshooting tips

Diagnosing starter problems can be simplified by following some basic troubleshooting steps:

  • Try turning the ignition key several times – Starters can sometimes get stuck and repeating the ignition cycle can free it up.
  • Check battery voltage – Use a multimeter to confirm battery voltage is at least 12+ volts.
  • Check battery terminals – Clean any corrosion from the terminals and cable clamps.
  • Perform a voltage drop test – This can identify excessive resistance in the starter circuit.
  • Bypass the solenoid – Use a screwdriver or jumper wire to bypass the solenoid and engage the starter directly.
  • Listen for noises – Grinding or high pitched screeching often points to issues.
  • Check for loose starter mounting – Loose bolts can cause the starter pinion not to engage properly.

By methodically testing different parts of the starter system, you can usually determine what component is causing the problem. This will help you fix only the failed part instead of replacing the whole starter needlessly.

When to replace a starter

In some cases damaged starters may be repairable, but it is often easier and more cost effective to just replace it. Here are some common situations when replacement is the best option:

  • Gear teeth excessively worn – Indicates damaged drive gear.
  • Solenoid failure – Difficult to repair, so it’s best to replace starter.
  • Starter draws excessive current – Signals internal short or component failure.
  • Repeated starting problems – Suggests multiple worn parts
  • Visible damage to housing – Cracked or damaged starter housing requires replacement.
  • Extremely high mileage – Starters have a lifespan around 100k-150k miles.

If your starter is causing frequent issues or fails to work reliably, replacement is probably the smartest solution. Installing a new starter can typically be done in an hour or less on most vehicles without much difficulty.

Finding the right replacement starter

Once you’ve determined that a new starter is required, it’s important to get the correct replacement. Here are some tips for finding the right starter:

  • Check OEM part number – Look up starter part number for your exact make/model/year.
  • Match mounting points – Replacement needs the same bolt pattern and size.
  • Check starter type – Mini, compact and full size starters.
  • Match electrical specs – Voltage, amperage draw, and solenoid type.
  • Compare gear teeth style – Different tooth profiles are used.
  • Review replacement brand – Stick with reputable brands for reliability.
  • Consult experts – Auto parts specialists can help match the right part.

Aftermarket starters from reputable brands will provide equal or better performance than the original for less cost. But always check specifications carefully against your vehicle to get the proper replacement starter.


Failing to start is one of the most frustrating problems you can experience with your vehicle. In most cases, starter issues end up being the root cause. Understanding the common causes of starter failure along with smart troubleshooting and replacement tips will help you get your engine turning over again. With some basic tools and automotive knowledge, you can diagnose starter problems and get back on the road.

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