2002 Chevy Astro – P1638 F terminal.

2002 Chevrolet Astro, V6 4.3, Stock.

Original Alternator at time of purchase was only charging 10v.
New alternator #1 charged at 14v, survived 200 miles.  Suddenly, dash showed no voltage, and no battery/charge warning light.  No obd2 generic codes.
New alternator #2, still no charge.  Was installed with a new and fully charged battery.  Bought new scan tool, and was able to get OEM P1638 F terminal code.  My scan tool has live data, but I don’t see the PID for F coil command/demand.

Checks:
Alternator + to battery – 12.2v. 
Battery + to battery – 12.25.
Voltage drop, Alternator + to Battery + 0.025
Voltage drop, Alternator case to battery – 0.00
F terminal to battery (brown?) (Key on Engine off) 1.7v
F terminal to battery (Key on Engine running) 1.7v
L terminal to battery (tan?) (KOEO) – 0.00v
L terminal to battery (KOER) – 0.00v – and no batter warning light on dash  (light does work on key on initially)
removed PCM connectors, all clean, no corrosion.

I find it improbable that I’ve received 2 faulty alternators (no, there was no bench test for the first failed unit)  With only 1.7v on the Field Wire (brown?)….. am I looking at a failed PCM?

any additional tests I can complete?

Stay dirty!