How to test for pending alternator failure

[WildernessJeep]

On my recent drive to Mexico I noticed something that can only be noticed with hours of south texas driving. My voltage would start very high (14-15 volts), then as I was driving would drop and drop down to about 12 volts. I also noticed when the A/C fans and headlights were on, the voltage would hover at or below 12 volts. These measurements are indicated on the dash gauges, not actually measured.


Anyone have a simple and easy way to test for a pending alternator failure on this vehicle? How to trick the voltage regulator and make it run wide open to measure the output?


Other signs of pending alternator failure? I know from experiance that running low voltage on a complex system like this truck will have bad and long-term effects on everything else.

 

[livingez_123]

you can take if off and go to any autozone and they will test if for free. It could have been just many hours of driving with the a/c and lights on and the alt just couldnt keep up with the draw.

 

[WildernessJeep]

you can take if off and go to any autozone and they will test if for free. It could have been just many hours of driving with the a/c and lights on and the alt just couldnt keep up with the draw.

And Autozone will 9 times out of 10 say "you need a new one". I've seen the counter people fiddle fart around with that machine enough that I wouldn't trust them to test a light bulb. Plus, Autozone parts are crap, and if it is sitting on their counter, they will want to sell me the new one.

Any other way to test it? My gut tells me this thing is dying. Who makes the best replacement?

 

[kschumake83]

Any idiot can run that machine it will be 1 connector 2 alligator clips, slide it on a rod and wrap a belt around it. It is so simple, just keep an eye on the person doing it and watch the screen, if it shows all green then it is good. I used to work at autozone as a second job when I first bought my house, and have tested quite a few that turned up good.

Sent from my Nexus 7 using Tapatalk 2

 

[livingez_123]

I know autozone saved my butt when I was clear across the US in FL in my dodge when my alt went tu it had 100k on it, I bought their lifetime warranty unit and they replaced it 4 more times in the next 500k. it worked great for me because I used my Dodge in my business and was going nationwide.

 

[angrysam]

What year is your vehicle? PCM controlled alternators will not be at 14VDC all of the time. MY 07 Avalanche would drop into the 12's for periods of time driving on long trips. The PCM will turn the alternator on and off as needed.

Volt meter across the battery terminals should indicate a charging alternator. It won't tell you how many amps you're getting though.