How to evaluate the functioning of the starter motor

It is always better to evaluate the functioning of the starter motor on a bench, because doing this operation on the vehicle can be dangerous. So once we have removed it from its housing, we connect one of the jumper cables to the negative terminal, and the other end to a metal part of the starter motor.

We will connect the other jumper cable to the positive terminal, and the other end will be disconnected from the starter motor, for now. We identify the power terminal - which is usually the smallest - on the starter solenoid, then using the crocodile clip with the wire, we connect the end of the positive terminal to the test battery, and briefly touch the other end of the wire with the crocodile clip to the excitation terminal of the solenoid.

If the solenoid is functioning, we should hear a "click" and the pinion extends outward, and consequently the starter motor starts to rotate smoothly.

If nothing happens, the solenoid may be defective. If you hear the click but the starter motor does not turn or does so slowly, there may be an internal problem with the starter motor, such as excessive friction or worn brushes.

If it works correctly on the bench but once reassembled it does not, then it is a problem with the vehicle's electrical system.