When does the starter motor need to be replaced?

You get into your car, and you want to start your engine but it doesn't want to turn over. This happens to many of us. Does this mean that your starter motor is bad? Not always. A bad starter motor is only one of the possible causes. How does it work?
Car Starter Motor Car starter motor.
A starter motor is attached to your engine. It's a small heavy duty DC electric motor that is powered by a car battery. Read more: signs of a weak car battery.

When you turn the key or press the button to start your car, the starter motor engages a little gear and turns over your engine to fire it up. Of course, for this to happen, your battery has to have enough charge and your auto transmission must be in Park or Neutral. Read more how a starting system below.

Are there any signs that a starter motor is going bad? Yes, but not always; sometimes a starter motor just stops working one day. In some cars when the starter motor is getting 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 that usual, even if the battery is fully charged or new. In some cars a starter motor may produce an abnormal grinding or whining noise 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? The old-day trick was to tap a starter motor lightly with a small hammer and see if it starts working after that. If it did, the mechanic would know the starter motor is 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 battery. If there is a battery voltage at both terminals when pressing the Start button or turning the key and the starter motor doesn't run, it's bad.

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

How long does a starter motor usually last? In some cars, a starter motor may last for the lifetime of the vehicle, but it's also not uncommon to see it fail after 5-7 years. Sometimes it happens in as little as 30,000 miles.

How does a starting system work in a car? First, the car computer checks if the code in the ignition key or the key fob matches the security system (immobilizer).
Car Starting system Car starting system
Then, the computer verifies that the transmission is in Park or Neutral or if the clutch pedal is depressed in a car with a manual transmission. If both checks pass, the computer operates the starter motor through the control circuit and a starter relay, see the diagram.

The starter motor is powered by the car battery and will only work if the battery has enough charge. A starter motor requires a very strong electric current to work. This current must flow from the battery through the cables and to the starter motor. This means that if the connection between battery cables and the battery is loose or has some corrosion, the starter motor will not work. For this reason, the battery and the battery terminals are always checked first if a car doesn't turn over. Read: Can a problem with battery terminals cause the vehicle not to start?
Car Starter Motor New aftermarket starter motor.

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 small 4-cylinder engine, the labor charge to replace a starter motor varies between $95 and $175. In some vehicles with large engines (e.g. BMW, Cadillac Northstar V8, Toyota V8), an intake manifold or other components must be removed to get to the starter motor and that requires a more labor ($260-$450).

An aftermarket starter motor (part) costs $85-$220 plus the core charge. The core charge is a deposit for an old part. Many part stores will give you the core charge refund If you return the old starter motor (core).
An original or 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 once in a while it would take a few tries for a car to start and 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, any local auto electric (Starter & Alternator) shop should be able to rebuild a starter motor. Prices range from $65 to $150 (not including installation). Of course, rebuilding a starter motor takes time.

If a starter motor gear does not mesh properly with the flexplate ring gear, a starter motor may produce a loud grinding 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. Beside a bad starter motor, this could be caused by worn-out flexplate or flywheel gear teeth. Replacing a flexplate or a flywheel is expensive, as in either case, the transmission must be removed.