Just curious, have you had this error re-occur yet? The reason I ask is I had this very same thing happening to my HHR SS on/off for almost 6 months. I think they finally nailed it down this time. It was in and out of the shop about 4 times, the last time for 11 days!
I was getting a P2138 code that current with mine and it ended up being a burned wire in the wiring harness. They had replaced the entire pedal assembly first, but that didn't solve it. This time they had to relace all of the leads between the throttle pedal assembly that went to the ECM. Looks like that was a total of 5 wires, but I do not know how many connectors.
Good luck!