2007 Mitsubishi Outlander Sport, Service Engine Soon Light comes back on after reset. The OBD reports an O2 sensor on bank 1. Replaced O2 sensor light comes back on around 55 miles of driving. Changed out again, same results. Mechanic talked to local Mitsubishi Manager, no idea what the problem could be. Anyone had this problem? We did check the gas cap for proper fit. Could it be the CPU is going out?