-95 GM Lumina APV Van with 3800 (3.8L VIN L)
-Intermittent loss of alternator/generator charging (particularly
when hot right after startup or unplugging and then plugging in
the generator control connector).
-Rare erratic shifting and PCM undervoltage code.
Specific symptoms all the time (even when generator working):
-Voltage at "L" terminal, when disconnected from generator, ~30mV
when ignition in 'RUN' position and ~10.5V when engine running.
Should be B+ (~12.5V) in both cases.
-Voltage at "L" terminal, when connected to generator, ~30mV
when ignition 'ON' and ~11V when engine running. Should be ~1V
and B+ (~13-14V) respectively.
Specific symptoms during failure (engine running, generator not
working because control voltage to low or erratic):
-Voltage at "L" terminal, when connected to generator, highly
erratic on scope (smear from 0 to 10.5V for 50ms and 10V for
10ms or constantly 0 to 8V) averaging 3-6VDC. Sometimes (very
rarely) it is stable at 9-10V that still does not allow the
regulator to turn on the alternator.
-Curiously; revving the engine usually kicks it out of this
failure mode into the ~11V generator control output.
-If driving and generator failing consistently this is sometimes
accompanied by erratic shifting or PCM going into limp mode or
PCM undervoltage code. This is probably when, due to loads and
the alternator not working, the system voltage drops to low.
-Generator/Alternator good; replaced unnecessarily :-(
-Generator connector (PLF/IS) OK
-CKT225 OK (Good impedance, no short to ground, 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 (checked as per TSB 23-81-06)
-Many other PCM outputs that should be at B+ checked and
-PCM swapped with loaner from dealer with no change :-(
I have been over the TSBs and large portions of the service
manual and am rather at a loss here. Something is pulling or
allowing the generator control voltage to go down. The PCM
power and ground is good and I have disconnected the blue
connector (red and white have to stay in since they have power
and ground) and as many sensors/outputs as I can get at to see
if one of them is dragging the output down; but to no avail.
A few remaining, long shot, possibilities include:
-Second, test, PCM also bad.
-Some sensor/output that I missed is dragging it down
This is similar to this problem that I found on the net:
but replacing the PCM did nothing. The dealer expert and I
are rather stumped. I am probably going to see about trying
a 3rd PCM. Any other ideas?