I just finished fixing my multi symptom mess on my 2010 Cobalt. If you are experiencing multi symptoms you must check through all the wiring harness under the hood. The plastic conduit on much of the wire harness was cracking and hardened. I finally found a clump of wires butted up against an edge of a part attached to the engine. The plastic conduit looked fine from first view, but when I was checking some wires for continuity I got some changes as I wiggled some wires and finally found those wires shorting onto the engine part. The short caused an engine manifold pressure code, an exhaust solenoid code , and a shift solenoid B code that was causing horrible transmission shifting problems. These were low and high circuit codes because those wires were shorting directly to ground and probably to each other. I coated the wires with silicon rubber and put new conduit on, and plastic tied them off of the engine. All problems solved.