How to test a starter motor

How to test a starter motor
How to test a starter motor

Starter motors have a hard job, and I have owned many cars where the starter motor has eventually needed to be changed. 

What normally happens is that you will jump in your car to go somewhere important, turn the ignition key and all that you here is a clicking noise and the car won’t start. Often, you may not hear anything, the dashboard lights come on but the car will not start.

Before you go ahead and strip the starter motor off the car, make sure that you have checked that the alternator and the battery are working correctly. Also make sure that you have checked that all of the wiring to the starter motor is securely in place. We recently had a Land Rover Freelander that would not start, turned out to be a bad spade connection fitted to the back of the starter.

In the past, I have changed a starter motor and an alternator only to find out that it was a faulty battery causing my starting problems. Also check that all the wiring to the battery, alternator and starter motor (including solenoid) are secure and that there is no corrosion on the terminals.

We will assume that all the other parts of the cars electrics are working fine and that you have already removed the starter motor from the car. See article, how to change a starter motor.

Starter motor basics.

The purpose of this starter motor unit is to start the movement of the engine when you turn the key in your ignition.  Here is a typical arrangement of a starter motor. The large cylinder on the bottom is the actual starter motor and the smaller cylinder on top is the solenoid.  The entire unit with both parts is referred to as the ‘starter motor’.  See the toothed gear on the left, this is what turns your engine to get it started. There are 2 actions of a starter motor unit, the first is to push that toothed gear forward so that it meshes with the engines flywheel, and the second motion is the rotating of that toothed gear so that it turns the flywheel/engine.  This is how all car engines are started.

How to test a starter motor.
This is a basic ‘bench test’ of the starter motor and solenoid off the vehicle. It is a basic test that should be done before you fit a starter motor, especially if you have purchased one from the scrapyard.

There are other methods of starter motor troubleshooting, these are more indepth and are not covered in this article. We have updated the video below and it shows how to test the operation of both the starter motor and solenoid – take a look.

Price up a starter motor for your car

What you need to test a starter motor ;
A well charged battery,
A set of jump leads.

During these test it is quite common for large sparks to be produced. Make sure you are in a clear area where there are no flammable liquids or other materials.
There is too much torque, the safest thing is to mount it in a vice if possible.

Testing the solenoid.
The Solenoid (small cylinder on top) controls the movement of the ‘starter motor pinion’ or the toothed gear that can been seen through the cutout. Connect the black jump lead to the negative (-) terminal of the battery and the other end to the body of the starter motor.

Now connect the red jump lead to the positive (+) terminal of the battery and touch the other end of the lead to the terminal on the back of the solenoid.  The solenoid should click loudly and throw the starter motor pinion forward.  The starter motor should not turn.

If this does not happen, then the solenoid is faulty.

Testing the starter motor.
Touch the end of the red jump lead onto the large terminal of the starter motor. The shaft should rotate strongly, if no then there is a fault and the entire unit should be replaced.

This video shows the starter motor being tested.
One more time Always take great care when testing a starter motor. These things produce massive forces, so don’t try and hold it in your hand when you are operating them. They are designed to turn engines, so don’t think you can hold one still easily.

Please leave a comment or advice for others