How do you know if its a bad Starter or Alternator?

How do you know if it’s your starter or alternator that’s causing your problem? Welcome to Mercie J auto care, where compassion and craftsmanship come together. I’m Rick Smith, master certified technician.
Let me first explain what an alternator does. An alternator charges the battery and it kind of keeps everything going so we’re not just running off the battery. For example, in a flashlight we just have a battery. It it goes dead, the flashlight quits and then we either recharge it or put a fresh battery in. A car when it’s running, the alternator should be charging the battery all the time.

There’s a couple things, if you have a voltmeter, watch that voltmeter. You turn the car on and it should be about 12 1/2 V starting up. Then the voltmeter should go up to about 14. The other thing you can do is most cars have some sort of a battery light but that battery light is actually an alternator light. So you turn the key on, you should see the battery light come on then start the car up and you should see the battery light go off. Typically that’s gonna be a good alternator and typically the light will come on if the alternator is bad.

There are some situations where that’s not true. With a starter, typically the car is either gonna crank over real slow or you’re gonna hit the key and you’re gonna hear a single click click click or you’re going to get nothing.

So that’s one way to kind of start to separate a bad starter from a bad alternator. Obviously the diagnostics get to be a little bit deeper than that but I hope this helps you out. Until next time, safe travels and blessings to you.