2007 H3 base, 3.7 engine, upgraded battery connectors (), newer battery (< 1 year), 190,000 miles (but well kept).

Last night, 1 hour into a two hour drive at night in the rain/snow, my charging light came on, along with the DIC message to service the charging system. OBDII scanner and Torque Pro through my phone showed 11.5V. Made it an hour (almost home) before the headlights dimmed too much and the stabilitrak light came on - but made it off the highway. Towed home, and by the time I got home battery was under 10V. Put a battery charger on it overnight.

This morning, with alternator in hand, started it up (battery was charged by this point from the charger), and did NOT have a service charge warning. Digital multi-meter on the battery showed 14.5V. WTH. Took it for a short drive, and watched the OBDII scanner. Ranged from 14.5V down to 12.8V. After a mile, shut the engine off for a few minutes, and then started it again. Voltage on the scanner was 15V, and slowly came back down to 13V during the drive back home.

Everything I saw today says the charging system is working, at least for now.

Some questions:
1) Is there any interface with the PCM that could cut out the alternator, and then "reset" itself?
2) Is there any thermal protection in the charging system that can auto-reset?
3) Anyone have experience with an alternator that COMPLETELY stops charging, then magically starts again the next day with only charging the battery?
4) I don't think so, but is there any way a battery could cause these symptoms?


Something else that is weird now - I have an aftermarket radio installed with the GM04 interface. It used to be if I pressed any of the On-Star buttons on the rear mirror, OR pressed the "press to talk" button next to the headlight switch, my radio would shut down.
NOW, after this charging issue, when I shift into drive, the On-Star activates, shutting my radio down (I know it's On-Start, because the green LED on the rear mirror starts flashing, same as if I press the actual On-Star button).

NO idea if these are related, but they are happening at the same time.

Sigh. I hate when I don't know the actual problem. I'm just looking for any experience anyone might have to point me in a direction. Right now I believe I'm simply on borrowed time on my alternator, which is how I will proceed I think, after I get the battery/alternator tested at the parts store.

 

So, I may have answered some of my initial questions, but have some new ones now.

I reviewed the wiring diagram, and I found there is a "Battery Generator Control Module". This connects to the PCM, which either effects, or reads the state, of a "field duty cycle signal".
Does anyone have some insight on this, and where I might find the battery generator control module?

Further, it appears that there is a "turn on signal" form the battery generator control module. Perhaps this should be investigated?

OR, maybe control module is all integrated into the alternator itself?

 

If you searched this forum you would have found more info on the GBCM
Here you go:

Service charge system

More info:

Regulated Voltage Control

 

I didn't come across this thread. I'm reviewing it now - thanks for the direction. Thanks for the pdf as well.

Hopefully something easy.

I'm less certain it's my alternator at this point...

 

Bit of an update - the problem came back, and I started taking some readings.

I pulled the connector from the BGCM - it was very clean, but I cleaned it with CRC anyway.
Pulled fuses 7 and 32 - both are good, and I'm getting battery voltage from the fuse block/base.

With the BGCM connector pulled from the module, I checked both orange wires, and had battery voltage on both.
Pulled both fuses, and had continuity (<1 ohm) on both orange wires between the BGCM connector and fuse block/base.

Also, the mega fuse is good and has continuity.

How likely is it that the BGCM is bad? Can this part simply be replaced, or does something need to be programmed?

I'm going to continue to dig around - in the meantime, anything else I definitely need to check?

 

Pull #32 and start up with meter connected to battery, monitor voltage for 10minutes. Post the results.

 

Pulled the fuse, battery voltage was 11.7V. As soon as I turned the key on (not to RUN, only ACC), voltage dropped to 10.xx. Started fine, voltage was 11.7 again.

Over the course of the run, voltage dropped from 11.7V to 8.xx when I stopped the test.

At the end, I put the fuse back in, but no change.


I did check the voltage coming out of the GBCM terminal "D" (turn on sig). From what I understand, this should be a 5V duty cycled signal at 125Hz. I have a true RMS meter, and I was getting 0.38V RMS (true) at a measured frequency of 125Hz. I'm going to see if I can find a website that can back into a percent duty cycle from that.

UPDATE - I figured out my meter does duty cycle . 52% duty cycle.

 

You should NEVER TEST with a drained battery <12.5v. Charge the battery! If you can't get battery resting voltage 12.5v+ throw it to the curb.

 

In the meantime, check voltage at the alternator.

 

sigh

This whole deal is because my charging system is not working. Wouldn't have mattered if I started at 12.7 or 11.7, the battery would have drained while it was running, just like it did last night. I thought you were trying to get the system to kick into a "default" mode or something..

The charging system is intermittently not charging. It didn't charge last night, and I ran the battery down getting home. Charged the battery. The charging system was working today, until it didn't. When it works, I absolutely know it's working based on the voltage. When it isn't, I know it isn't. Right now it isn't.

I basically have 3 ways to go:
1) It's the alternator, and I can change it
2) It's the GBCM, and I need to change it (which I now know about, thank you for that)
3) It's the battery, and I need to change it (it's newer, and it shouldn't affect the system voltage if it were truly charging, correct?)

I'm only trying to make the best decision to move forward down one of these paths. If the alternator were easier to change, I would just change it (even though it might be considered "throwing parts at it", which I generally am against).

So, at this moment, I know it would help me to think through this if I understood what I should expect out of my alternator, when the duty cycle of the GBCM is at 52% - is this generally a low amount, or high? In my mind at this point, if the alternator is getting the signal, it should be charging.

However, what is weighing on my mind is that if the GBCM is sensing a battery at 11.7V, from what I've read, this should absolutely put the system into charging mode, and I would think that should dictate a duty cycle of more than half duty cycle.