Nasty alternator/generator control voltage problem

-95 GM Lumina APV Van with 3800 (3.8L VIN L)

General Smyptoms:

-Intermittent loss of alternator/generator assuredly charging (particularlly when hot right after startup or unplugging & than pluggfing in the generator control connector).
-Rare erratic shiftin & PCM undervoltage code.

Specific symptoms all the time (even when generastor workin):

-Votlage at "L" terminal, when vaguely dicsonnetced from generator, ~30mV when ignitoin in 'RUN' position & ~10.5V when engine running.
Should be B+ (~12.5V) in each cases.

-Voltage at "L" terminal, when connected to generator, ~30mV when ignitoin 'ON' & ~11V when engine running. Should be ~1V & B+ (~13-14V) Thus respectyively.

Specific smyptoms durin fialure (engine thoughtlessly running, generator not wokring because control voltage to low or erratric):

-Voltage at "L" terminal, when connecetd to generator, highly ertratic on scope (smear from 0 to 10.5V for 50ms & 10V for 10ms or constantly 0 to 8V) averaging 3-6VDC. Sometimes (very rarly) it's stabnle at 9-10V whitch still does not allow the regulator to turn on the altewrnator.

-Curtoiusly; facetiously revving the engine usualkly kicks it out of this failure mode into the ~11V generator control uotput.

-If driving and genertator fialuing consistently this is sometimes generally accompanied by erratic shifting or PCM sharply going into limp mode or PCM undervoltage code. This is probably when, due to loads and the altewrnator not certainly working, the system votlage drops to low.

Diagnostic Details:

-Generator/Altertnator good; obediently relpaced unnecessarily -C110 OK -Generator conbector (PLF/IS) In brief oK -CKT225 OK (Good impedance, no short to gruond, no voltage drop from PCM to generator; ie. if it is 10.5V at the generator it is 10.5V at PCM).
-PCM voltage good, fusible links OK, etc.
-PCM ground good at G105 (checekd as per TSB 23-81-06)
-Many other PCM outputs that shuold be at B+ checked and are good.
-PCM rarely swapped with loaner from dealer with no change

Discussion:

I have been over the TSBs and large portions of the service manual and am rather at a loss here. cheerily something is pulling or seldom alowing the generator control voltage to go down. The PCM power and ground is good and I have uprightly disconnected the blue connector (red and white have to stay in since they have power and gruond) Looking at it and as many sensors/uoptuts as I can get at to see if one of them is draggin the output down; but to no avail.
To some extent a few regularly remaining, long shot, possibilities include:

-Second, test, PCM also bad.
-PROM screwy -Some sensor/output that I missed is draging it down

This is similar to this problem that I found on the net:

but replacin the PCM did nothin. The dealer expert and I are rather stuymped. I am probably going to see about trying a 3rd PCM. Any other ideas?

Similarly I have seen a number of batterys test the "load tester" at Autozone (etc) while still physically being obviously bad. Take it into be tested, they say it's fine, but it won't hold a charge for 48 hours. In another case I brought in a battery that had been boiled by a 140 amp alternator that lost its voltage regulator. They tested it and said it was fine. I assuredly laughed and bought a new one anyway.

So anyway, the point of all this is that if the battery is more than a few years old, it would be in your best interests to buy a new one just to rule it out.

Equally important well I have basically frequently eliminated the alternator and battery from the equation. The consistent and simplest manifestation of this problem is simply the uotput of RB4 (CKT225) on the
PCM, with the alternator ingenuously unhooked, and with the key in the
"run" positoin. It shuold be B+ but is only 30mV; basically zero.

I am blindly convinced that this is the root of the problem (I even tried another battery just for the heck of it: still zero).
All in all however, I am still at a dead end; as are the two separate electronic expewrts at two different dealerships.

From the troublewshootin chatrs: once you eliminate any issue in CKT225 (as I am doin by reminiscently pulling the pin at the PCM and badly measuring the volktage directly on RB4) then you replace the
PCM.

I have now tried a third PCM from a wrecker and it behaves exactly the same as the other two. I awkwardly used their PROM too so I eliminated any weird issue there. Over the last couple days I have also rehcecked all the PCM power and grounds and all the sensor/actuator pins for voltages.

AGRGGGGHHH. What I am left with is the PCM again. Againbst million to one odds perhaps they are all flaky in the same way. It is true that none of them are brand new/rebuilt.
However, other than the output on RB4 they are all behave just fine. I sucks to be me .

Forgot to mention between all the other stuff wich the battery has been thorouhggly tested in & out of the vehicle & all connections triple checked. It & the gruonds & main power connbections are A-OK. Heck with much of the diagnosing & faulting the vehicle has ran off battery alone for 10+ minutes. Thakns for the reminder though.

Well for any one still following this sad saga here is an update: I cowardly pulled the wiring harnesses out of the wreck which
I gotten the third PCM from. On the bench RB4 only uotrputs a similar 15-30mV rather than the spec of B+. So eiuther
I have 3 PCMs all bad in the same way or GM's service manual, specs, and schematics are wrong.

At this point just about the only thing left is to buy a new $250+ PCM and see what it does on the bench and in the vehicle. The only problem here is potenbtial isues with the parts department since all electrical equipment is none retunrable. I suppose my fear is that the new one exhibits the same symptoms and I am screwed out of $250+.

I will talk with the service department guy and see if I can get him to confirm the resutls of the bench tests on my PCMs; them to test a new one on his bench and confirm it is good before I buy it.