You need a tuner or a flasher program like SCT to disable the rear 02's. If you have the original 02's it could be the 02 itself malfunctioning. To eliminate if it is an 02 or a MIL I would swap mils and see if it happens. If it comes on as bank 2 sensor 2 It is the mil, if it comes on bank 1 sensor 2 it could be the sensor.
Hope this helps
Hope this helps