How to test charging system

terrylee
Posts: 1
Joined: Tue Feb 26, 2013 3:06 pm

How to test charging system

Unread post by terrylee » Tue Feb 26, 2013 3:10 pm

2004 trailblazer how do i test alternator out put

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ProTech
Posts: 651
Joined: Wed Oct 17, 2012 10:08 am

Re: How to test charging system

Unread post by ProTech » Tue Feb 26, 2013 8:13 pm

This isn't something you can do with basic hand tools. There are a few different tools that shops and dealerships use to test the charging system and alternator output but more than likely you don't have any of them.

The only way you can check to see if you're getting any output at all is to check the voltage at the battery while the vehicle is running. You will need a voltmeter to do this. You should have about 13.5 to 14.5 volts if the alternator is working, depending on the electrical load on the vehicle. You will have no way to check the amps since it should be putting out around 70 amps under load and no consumer voltmeter can go that high without blowing. You'd need a special tool called a VAT40 or other charging system tester to really find that out.

If you think you have a problem, you might want to get it checked out rather than try to diagnose a problem yourself that you may not have the right equipment to do. Most reputable shops will do a starting and charging system test for free.
GM Dealer Technician For 18+ Years
In the automotive industry for 20+

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