I'm having some difficulties with my 2000 2500 6.0L Silverado. The alternator is not charging the battery.


Some Conditions:

When the truck is turned off, the voltage at the post on the back of the alternator matches that of the battery.

When the truck is turned on, the voltage at the battery is 10.5-12 volts (depending on how run down it is), but at the post on the back of the alternator I am only showing 3 volts.

If I unplug the weatherpack connector on the alternator, the back post on the alternator goes back to matching the voltage of the battery. Checking the voltage of the single wire in the alternator weatherpack connector I get a negligible voltage, less than 1 volt (like .005 to .01v). I'm pretty sure this voltage should be higher, like at least 5v, I checked on an '05 silverado and it was spitting out ~10v.


I've changed out the battery and alternator with new/known good ones and still have the same problems. I did a glance over of all the fuses under the hood and on the side of the dash and only found one that was blown. it was 'LT TURN'. I replaced it with a new one and I still have the same problems.



Does anybody know what the pinout is on the PCM for the alternator signal wire?

Are there any other sensors/fuses/wires anywhere else that I should check for?


This problem just arose, it has been working fine, then yesterday just stopped charging alltogether. It's really got me stumped so far. Any help would be greatly appreciated.

Thanks

 

After looking at my truck and my GM tech manual (99 silverado), the 4 pin connector only has one wire in it and it goes to the indicator lamp. You might want to check the wire from the back of alternator to the pos wire. This wire is a fusible link and in my opinion should be replaced with a larger wire.

I had almost the same problem, battery was not charging at all but the voltage at the alternator terminal was 14~15 volts (running), so I replaced my pos wire. I used 2/0 wire from the battery to the starter and 4 gauge from the alternator to the battery.

The last time I replaced my alternator I went through 4 alternators over 2 days. The first 2 came from Autozone (rebuilt) and both did not work, the next day I went to OReillys' and ended up getting 2 (rebuilt) from them, these also did not work. After the 4th alternator, I broke down and bought one from the dealer and have not a problem with it, I came to the conclusions my truck only likes AC Delco alternator (new). This sounds really crazy but those rebuilt alternator are something not that good.

 

Once i was able to get a look at it in the daylight i almost immediately figured it out. Apparently something got hot inside the little red positive connection box and it melted part of that plastic. The melted plastic got in between all the terminals connected to that stud so they were getting a negligible current through it when under a load. I pulled it apart and cleaned the terminals off and wala... it's back to charging again.