2004 not charging

[Rukee]

Hi all, I have a 2004 Envoy with the 4.2L that will not charge the battery and the battery light is on. I replaced the alternator with a new one and it's doing the same thing. On advise from NAPA I swapped it out again with another new (rebuilt) with the same results. Charged the battery, checked all the fuses under the hood, tested for baterry voltage at the back of the alt and it does have battery voltage there. What else could be causing this issue?? Thanks for any input.

[gmtech1]

Have you checked the battery with a meter to verify a no charge condition? Be sure to check it with the engine running, should be around 14v. It's possible the alt is charging, but the light is staying on due to a problem with the cluster or the pcm...

There may even be a code set.

[Rukee]

Thanks for the reply. Battery voltage does not increase when the engine starts, it's at or under 12v.

[mechanic1980]

make sure the battery is good some vehicles use the pcm to regulate alternator output and if the battery falls below 12.2 v the alternator wont start charging

[Rukee]

I'll try to swap out the battery with the one out of my GMC pickup truck and see if that helps. I'll report back my findings. Thanks!!

[Rukee]

Okay swapped out the battery with the one in my `95 k1500 which is less then 6 months old, charged the battery, starting voltage was at 13v, start the truck and the battery voltage drops to 12v. Still no charge

[maxwedge]

As I am sure you now are aware of, this is not a easy diagnosis/repair. If you want to continue to try and repair this yourself you will need an oe shop manual and follow the trouble tree for this condition, the pcm is part of the charging circuit control on modern vehicles. Alldata.com has a one year online subscription cheaper than the GM manual.