So last week truck died. Went to jump and couldn’t so I took the battery back home, charged it then went and brought the truck home. When I get it home my charger says low alternator and I have 12 volts! I shut it off and turn it back on and my charger says alternator works just fine and I have 14.4 volts. I check on my gauge in the truck and it says same.

my wife went to work yesterday and it died on the way home. Same thing happened. Charged up the battery and had my gauge saying 11 on the way home. Started the truck up an hour later and gauge reads 14.4 volts again. Charger said same thing as before!!


only thing I’ve noticed different in the last 2 months is i changed the heater core, it’s gotten very cold, and the gas gauge stopped working! Actually when the voltage says 11 the gauge says full. When the voltage says 14.4 the gauge says empty.

im thinking maybe pcm short. Idk. Cables are clean and everything works fine then later doesn’t work!!!

Any ideas would be great.

 

That would be volts, not amps. What are you driving??

 

Fixed the typo. 99 dodge ram xlt

 

Voltage regulator is part of the PCM, never thought that was a good idea, but, they didn't consult me when designing it. Check all your connections first, make sure everything is clean and tight, if that all checks out, you can have the alternator tested, off the truck..... and if it passes, new PCM time.

 

There's write-ups on how to convert to a standalone regulator. I've never done it but a web search WILL get you there. It's common enough on these trucks that others have tackled it before.

 

How many miles on it? Mine was the original alternator and got around 240K on it before acting up. Check the battery terminals with vom to check voltage don't trust the one in the truck. There is a fuse in the pdc for the alternator, It's probably not bad but wouldn't hurt to check it out.

 

Well positive voltage drop test was 11.7 or something ??? Went from positive post to post on back of alternator.? Is this correct.

That’s like not Evan connected.? Or is my brain not working as usual. My load test on the battery with no alternator working was like 12.5!

obviously it’s a little over 5%. Or am I wrong on my drop test?

 

Well cleaned em up nothing changed.

 

What gauge?
A lot of things can cause no/low charging. Need to rule them out before assuming it's pcm. There is a test for that also.
#1 how many miles on the alternator? High miles the brushes could be worn and not always making contact.
#2 Did you check the belt tensioner? They tend to freeze up and not keep tension on the belt. belt slips alternator doesn't charge.
Check battery voltage at the battery with a vom(volt ohm meter)positive and negative terminals. With the truck off should be around 12 volts. Start the truck voltage should go up to around 13.5 volts. Turn all the lights on and see what voltage you have.

 

I checked the volts I’m about 12.5 -13 on the new battery and 12 when it’s running. So I did a voltage load test. Ground was .2 everywhere. Positive was 11.7. Evan said 14.1 for a little while???

i went from the positive post to the post on the alternator. Is this correct for a voltage load test!