Load Testing Alternator On Vehicle

I made a brief video on the procedure I have used for many years here at the dealer that has not failed me yet in identifying a weak but functioning alternator causing many headaches like no starts after changing the battery and only checking the voltage output of the Alt. I hope this helps as there really isn't a need to take the alt off to get it tested. No fancy tools required.

Alternator Load Testing On Vehicle - YouTube

TLR Common alternators cahrge at about 14.5v nominal. some at 15 to 13.5 a charged car batt usually sits at about 12.9 to 12.7. lower than that and CCA begins to suffer.

if the alt drops below 13 you have a weak/failing alternator.


test process.

1. Multimeter connected to battery reading voltage.
2. engine at warm idle (below 1k revs )
3. verify idle voltage is above 13.0 (our 1st gens are about where the vid shows it to be)
4. headlights on, watch voltage. should dip and recover or stay the same
5. heat/ac fan on high setting, rear ac fan on high setting
6. rear def on heated seats on if you have them.
7. any other things you run on your daily drive.

what you want to see is the voltage drop maybe to 13.5 for less than a sec then recover to at least 13.7 to 14.0 - 14.9

great info! thanks!

sorry wrong thread.