How To Test An Alternator

Below is a video on how to test alternator

If you could subscribe or like the video…. thanks. I hope this helped someone out there. If you know someone that it could help just press the share button and share it with them. Be sure to check back soon for do it yourself fixes soon.

Today we will be showing you how to test an alternator. We will be showing you on a 2001 Subaru outback but it will work the same on almost every car. So to start you will need to pull the hood release and then prop the hood open with the prop rod. Once you have the hood open we can locate the battery within your car. On this Subaru it’s close to the front and located on the drivers side.


Once you located the battery you will need a multimeter. Set the multimeter somewhere flat or clamp it onto something if is the multimeter with the clamp. Make sure where you put it the multimeter or wires can’t fall into the pulleys. Also be sure that the leads can reach the battery. If your meter says dcv you want to set it to 20 since we will be working with 20 or less volts with these charging systems.


With the multimeter in a safe place we can take the positive and negative leads and touch the positive lead to the positive side on the battery. Make sure it makes a good connection. Next take the negative lead and touch it to the negative side of the battery. If you have a good battery it should read close to 12.6 volts give or take a bit. Now having a lower reading doesn’t necessarily mean your battery is bad. It could be lower because the vehicle has been running off the battery because the alternator is not charging properly. 


Once we have that reading what we are going to do next is start the car let it run for a little bit till the idle stabilizes. Turn the meter on and then take the test leads again and touch the positive and negative leads and touch the positive lead to the positive side on the battery. Next take the negative lead and touch it to the negative side of the battery just like we did before. Make sure they both makes a good connection. You should get a reading of 14.2 – 14.7 volts somewhere within that range would be a good reading and will tell you that your alternator is working correctly. If your reading is over 14.7 it means your alternator is over charging which is not good for the charging system or the battery. If it’s below 14.2 let us say 13.2 it will still charge the battery but once you start using accessories such as the a/c, headlights, defrost ect. it will most likely make it dip below 12.6 and will not be enough to charge the battery.


If you end up getting lower then 14.2 there are a few things to check before you go and replace the alternator they are inspect and ensure that the battery cables are tight. Also check to make sure there is no corrosion if there is clean battery cable ends and posts on the battery with a battery terminal cleaner. Also check the connection on the alternator and plug on the alternator to ensure there is no corrosion on them and that the plug is clicked in and tight. If you have any of these correct them and redo the test to see if it is within the range of 14.2-14.7. If it’s still not within the range then replace your alternator with a new one or a remanufactured one. So that’s it we have just showed you how to test alternator.







Leave a Reply