Engine/Transmission (1998.5 - 2002) Dead Alternator

[Batphreak]

Yesterday, went to the store to get food and such everything with the truck was fine. Start up and head home, "Check gauges" light stays on because the charge voltage is low. I checked with a multimeter when I get home, yup only about 11V. Pulled the battery cables off and the batteries are OK, about 11. 5V, but the were getting discharged by AC and such. So, pulled the alternator off (after checking the 140A fuse just to be sure) had it tested at Autozone (only place open on Sunday) it was junk. Bought a reman with lifetime warranty and put it on. Everything seems fine now, batteries need to charge a little, but if I rev the engine I get just at 14V. I'm a little leary of Autozone's tester, though since the alternator is controlled by a voltage regulator in the PCM, and I know on older vehicles Alternators and regulators had a habit of taking each other out. Anyone think I should still be worried that I'll have to get a PCM yet? Not a single code is in the PCM so I'm guessing it's ok.

 

[Missouri Mule]

The EVR which is the PCM control the charging rate of alternator.

On the 12 valves 2nd gen the EVR gets input from the ASd relay (line voltage)and the Battery tempature sensor (explains itself).

Don't know what supplies line voltage to EVR on 24 valves (but something does).

Battery tempature sensor tell the computer the temp of battery. When battery is cold the EVR will increase charging rate and when warm decreases charging rate (Book refers to it as system voltage).

So if you are at operating temp 14 volts should be Ok.