Took it to the dealer since I was still under the 5yr/100k mile powertain warranty. Dealer said there's a memo out that this code with these symptoms on 2012 Volts means the cylinder head needs replaced, so they're doing so. Part should be in tomorrow. I wonder if they fixed whatever caused this to happen in the first place. If not, might be selling this. No way I want to have to pay for this again out of pocket! Probably not a cheap or easy fix.