Then check your cig lighter fuse, it supplies the OBD port.

 

Don...now that's an interesting suggestion. I do use that cig lighter for cell phone charging. And that charger plug flickers as if not good connection. I wonder if that charger is somehow interrupting current to the point that it would cause these issues???

 

Disconnect it and see if that’s the issue, let us know!

 

I didnt do anything to cig lighter fuse....just removed the phone charger and took for a short drive on city streets and freeway a few miles. So far all readings normal I guess. No misbehavior. I am losing 1 volt between CM and adapter plug consistently at any rpm. CM is getting 14.9=15 volys and adapter 13.8-14 volts.

Time will tell.

 

That’s what I was referring to remove the phone charger, as you have. Thanks for your follow up.

 

So, I went way out on a limb and drove the car in the middle of southern california rush hour commute morning and evening 85 miles each way. With no phone charger plugged in. I also installed fresh fuses in the engine compartment ECM and Trans CM locations because the old ones exhibited some corrosion on the prongs. With OBD in and reading Torque all the way, the CM volts maxed out at 14.9 and AD at 13.9 and after driving a while and idling in traffic, the CM volts occasionally dipped to 12.9 with AD at 11.9......made me a little nervous but the car did not freak out and made the round trip without issues. Not sure if its fixed or just lucky. Question....what about the charging port in the rear of console? If a charger was plugged in there, is it on same circuit as cig lighter?

 

I don't know what car Oldblue is looking at, but that isn't a 2009 HHR fuse block. #33 is the EXH (o2 sensors)

The front aux power outlet is #29 under hood and the console is on #30, nether are cig lighter unless you have the smoker package RPO.

The alternator output changes dynamically according to demand, That is what the current sensor on the negative cable is for. The only voltage reading that matters is the one on the OBD2 port.

 

Well, 2nd day of trial driving and so far no stumbles or issues. the adapter at the OBD port is 1 volt less than CM no matter what. I've seen it dip to 11.5 but no lights or engine stalls yet. Not sure. I'm electrically challenged.

 

Another follow up here. After a few weeks of fairly uneventful commuting in my HHR, things took a dump couple of days ago and persist. The rough idling returned. But now getting all sorts of new codes and dash lights. Driving down freeway the other day, the car suddenly displayed "engine speed reduced", "service ESC", check engine light .......I pulled over, reset and cleared and headed home. It repeated within 10 miles. Tried again today and it started giving me 0300 " random misfire" code as well as p2135 " throttle position A/B voltage correlation" or something like that. Went into limp again. Got it home and parked it. I'm kinda thinking of just changing out the alternator to remove it from equation. ????

 

You could have it bench tested, to confirm it’s the problem.