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This p-code is pointing to a fault with the internal heater for the rear oxygen sensor. The PCM uses this heater to get the sensor to normal operating temp within a matter of seconds on cold starts. Replacing this sensor should solve the problem. This sensor is located mounted to the catalytic converter. The best access is from under the vehicle.
When replacing this sensor, you do not need to worry about where it connects to the ECU. With this p-code, replacing the sensor itself should do the trick. Follow the electrical connector up from the sensor, and you will find an electrical connector. Simply unplug it, and remove the sensor. The new one will have the same connector. Install it into the catalytic converter and plug it in. You should be good to go.