How to Diagnose a Bad Starter Motor

Imagine coming out to your car in the morning, turning the key while you’re all set to go to work and it doesn’t crank over. Nothing happens at all. We’ve got several possibilities that could cause a problem like that. One of the things that might be suspected is a bad starter motor, so we’re going to take a look at some of the procedures that would take place in order to determine if the starter motor itself is bad. The first thing we’re going to start by doing is making sure that the battery is good. We’re going to perform a load test on this battery by hooking up this volt amp tester to the battery hookup (which is very much like hooking up a set of jumper cables).

Then we can see that the battery is 12.5 volts, which is a good thing to start with. Based on the batteries, it’s at a 300 cold cranking APP rating. We’re going to adjust the load knob, which applies a load much like a starter would up to 300 apps. Then we’re going to see if they can keep the voltage up. We do this for 15 seconds. At the end of the 15 seconds, it is still over 9.6 volts. This battery should have a sufficient capacity in order to start this vehicle. So the battery’s not the problem.