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How to Test a Starter Motor (Step-By-Step Case Study)

Starter Motors

David Taylor

28th Feb 2018

Starter motors are a common component in the majority of cars and their main function is to help start the engine. Due to this key role in the ignition process, if the starter motor breaks then it’s unlikely you’ll be able to operate the vehicle.

But how do you know that it is actually the starter motor that has failed? What are the common signs of starter motor failure? And, most importantly, how can you test a starter motor?

To help, we’ve spoken to our in-house engineers here at QX Components. With over 28 years of experience in the starter motor and alternator business, our engineers are one of the most qualified sources on everything starter motors.

Note: Like we’ve said before, starter motors can seem like complicated tools but, if you understand the jargon, they honestly are quite simple components of your vehicle. Understand the technical terms using our jargon buster here.

Testing the Battery

Whenever you are dealing with a dodgy starter motor, the first place to start looking for issues is the car battery. The car battery plays a key role in the operation of the starter motor and if the car battery begins to fail it’s likely the starter motor will fail too.

Corrosion or Loose Terminals

image showing acid corrosion on a car battery

If the terminals on the car battery start to come loose this could result in corrosion from seeping battery acid. This will eventually lead to a lower than optimal voltage being sent to the starter motor and the starter motor will fail.

The solution to this problem is simple. Ensure the terminals are tight and clean any corrosion or acid away from the battery.

Battery Voltage Test

If you own a digital or analogue multimeter then you can conduct a battery voltage test.

If you’ve never performed a car battery test before, watch the video below.

image showing a user performing a car battery test

A good battery in full working order will show 12.6 volts. The bare minimum a car battery can get away with is 12.3 volts. Please note that if the car battery is testing below 12.3 volts then you will need to either charge the battery or replace it.

Test the Solenoid

If the car battery is in good shape, the next test involves the solenoid. For those not clued up on starter motors - the solenoid is a small component housed above the starter motor. The solenoid provides a large current to the starter motor. Without this large current the starter motor will not be able to operate and crank the engine. For more information on how a starter motor works read our complete guide here:

image showing a solenoid

Note: You will need a friend or family member to help you conduct this test.

Step 1: Locate the Starter Motor

The starter motor is usually located near where the engine and transmission meets. The starter motor itself is a cylindrical shape with a smaller cylinder attached above. See the picture above if you need further direction on identifying the starter motor.

Step 2: Listen for the solenoid to click when the key is turned

The next step is why you need a friend or family member to assist you. With a partner in the car, position yourself near the starter motor. Now have your friend turn the ignition. You should be able to hear a click. This is the sound of the solenoid transferring electricity to the starter motor. If you can’t hear a click then the solenoid is not properly engaging. This probably means you need to replace your starter motor.

Test the Wiring Connection

Loose wiring connections are a mechanic’s best friend. How else can they charge an hour worth of work for a 5 minute job? Before you run off buying a new starter motor or dragging the car down to the local mechanics garage, check out the three key wiring connections attached to the starter motor.

Ignition Wire

Also referred to as the trigger wire, this is a small red and black wire that runs from the ignition to the solenoid via the trigger switch. If this wire is loose, then obviously, the signal will fail to be received by the solenoid and the starter motor will fail to start.

Battery Wire

Another important wiring connection, the battery wire is a key component in the operation of the starter motor. Make sure to check that all wires leading from the battery to the starter motor are in good condition and that the wires are fitted correctly.

Alternator Wire

Although it doesn’t necessarily play a key role in cranking the engine, a loose alternator wire could be shorting the connection on the starter motor. Check that this wire is not loose or damaged.

Test the Ignition Switch

Starter motor failure and ignition switch failure present quite similar symptoms. One key check, that can help you identify the difference between the two, is to see if the oil, brake and charge light function is present at position two. If the lights fail to turn on - this could be a sign of electrical issues in the ignition switch.

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