is there an access panel for fuel pump under backseat on 2009 cobalt?

Hello, Unfortunately, no. You have to remove the fuel tank. It is not too bad of a job, but make sure to diagnose the fuel pump before getting into it. It may have a bad relay, bad fuse, or bad circuit. Ensure power is getting to the pump, power it externally if you have to, and ensure it has failed before dropping the fuel tank. I would hate for you to get it all back into the vehicle to find a bad relay or fuse.