Ok I have resorted to the cobalt forum after pulling my hair out. I have a 2010 chevy cobalt basic package 2.2L. 69k. I'm having issues with reduced engine power/engine disabled with a code p0641 which is the 5 volt reference. The funny thing is it only happens when it's cold and now it's winter and always cold it's happening more frequently. I've replaced the ecm, new battery, removed throttle body and cleaned checked all grounds and cleaned. Checked harnesses for exposed wires, tested sensors with a multimeter a checked all connections. Has anyone had to deal with this ridiculous issue?? ? Thanks for any input!