Car sometimes doesn't turn on?

Yes, your jumper wire could be causing other problems. I'm not sure what its for, but i would never mess with the wiring harness on a modern car. First make sure your battery is strong and that all connections, including the several different grounds on the car are clean and tight. Scan for trouble codes. There is probably information stored in your computer that will guide you. Don't start replacing parts until you know they are faulty. Just because the computer says a certain sensor is not working does not mean its the sensor. It may be bad electrical connections making the computer think its faulty. Sometimes the best money you can spend is money spent at a shop that specializes in automotive electrical systems. Good luck. These sort of problems can be frustrating. PS: Search through the Cobalt threads here. There have been lots of discussions about this sort of thing with lots of fixes that seem to have worked for at least one or two people. Things like replacing a certain fuse or adding a ground wire somewhere. My own electrical glitch in my '06 SS is to switch the headlights to high beam for a couple of seconds. Restores my gauges and power steering every time.