When does the starter motor need to be replaced?

Updated: May 18, 2020
The starter motor is a heavy-duty electric motor powered by the battery. It turns over the engine when you want to start it. If a car doesn't start, does it mean that the starter motor is bad?
Car Starter Motor Car starter motor.
Not always, a bad starter motor is only one of the possible causes; read how the starting system works below.

What are the signs that the starter motor is going bad? Sometimes a starter motor just stops working one day with no prior signs. In some cases, when the starter motor is going bad, you may notice that the engine won't turn over on the first attempt; it may take several tries before the starter motor engages. Sometimes a worn-out or shorted starter may turn over slower than usual, even if the battery is fully charged or new. In some cars a starter motor may produce abnormal grinding or screeching noises when it's going bad. Another sign is when at times a starter motor won't crank the engine when hot, but works fine when it's cold.
How do mechanics check a starter motor? In the old days, the trick was to tap the starter motor lightly with a small hammer and see if it starts working after that. If it did, a mechanic knew the starter motor was bad. Today, mechanics simply measure the voltage at the starter motor terminals. A starter motor has two wires connected to it: a small wire for the control circuit and a larger cable that is connected to the positive battery terminal. If there is a battery voltage at both starter terminals when pressing the Start button or turning the key and the starter motor doesn't run, it's bad and needs to be replaced.

Why does the starter motor fail? It has several moving and rotating parts inside. Over time, things like electric carbon brushes, bearings or an overrunning clutch wear out.
The electrical contact points inside the starter solenoid can also become pitted or burned. When the contacts inside the starter solenoid are bad, you'd hear a single click from the solenoid, but the motor would not run even if the battery, cables and the cable terminals are good.

How long does the starter motor last? On average, a starter motor lasts for 100,000-150,000 miles. In many cars, the starter motor lasts for the lifetime of the vehicle; however in some cars, it can fail prematurely.

How does a starting system work in a car? First, the car computer called PCM checks if the code in the ignition key or key fob matches the security system (immobilizer). If not, the security warning light will stay on and the starter will be disabled.
Car Starting system Car starting system.
Second, the computer verifies that the transmission is in Park or Neutral or, in case of a manual transmission, if the clutch pedal is depressed. Tip: Check if the transmission indicator displays that the transmission is in Park or Neutral; if not, the transmission range switch could be bad.
If both checks pass, the computer operates the starter motor through the control circuit and the starter relay, see the diagram. This means that the control circuit must be in working order. If, for example, the control circuit connector at the starter solenoid is corroded, or loose (which is very common), or the starter relay is bad, the starter motor will not operate.
The starter motor is powered by the car battery and will only work if the battery has enough charge. Read more: Signs of a weak battery. The starter motor requires a very strong electric current to work. This means that the battery cables must be in good shape and have good electrical connections to deliver the current to the starter motor.
Corroded vs Serviced Battery Terminal Corroded versus serviced battery terminal.
Often, the starter motor does not operate because the positive or ground cable connections between the starter motor and the battery are loose or corroded.
If the starter motor doesn't work, the battery must be tested first and the battery terminals and cables, as well as the control circuit, must be checked. Read also: Can a problem with battery terminals cause the vehicle not to start?
If the starter motor does turn over the engine normally, but the engine doesn't start, the problem is not in the starting system, but somewhere else (e.g. no spark, no fuel, low compression, etc.).

How much does it cost to replace a starter motor? In an average front-wheel drive car like Honda Accord or Toyota Corolla with a 4-cylinder engine, the labor charge to replace a starter motor varies between $95 and $175.
Car Starter Motor New aftermarket starter motor.
In some vehicles with larger engines (e.g. BMW, Cadillac Northstar V8, Toyota V8), an intake manifold or other parts must be removed to get to the starter motor and that will require more labor ($260-$450).

An aftermarket starter motor (part) costs $85-$220 plus the core charge. Many part stores will refund you the core charge if you return the old starter motor (core).
An original (OEM) starter motor is more expensive ($270-$480).
For example, one of our friends decided to replace the starter motor in his 2014 Honda Accord. He said that once in a while it would take a few tries for a car to start and that the problem was getting worse. He paid $390 for an original part plus $127 labor at the dealership.
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Can a starter motor be rebuilt? Yes, a local auto electric (Starter & Alternator shop) should be able to rebuild the starter motor. Prices range from $65 to $150 (not including installation). Of course, rebuilding a starter motor takes more time.

If the starter motor gear does not mesh properly with the flexplate ring gear, the starter motor may produce a loud grinding or screeching noise when attempting to start. In this case, both the starter motor and the flexplate (or flywheel in a manual transmission) ring gear must be inspected. Besides a bad starter motor, this could be caused by worn-out flexplate or flywheel gear teeth. Replacing the flexplate or flywheel is more expensive, as in either case, the transmission must be removed.