Front Oxygen (A/F) Sensor: Removal

Disconnect the ground cable from battery.
Lift up the vehicle.
Disconnect the connector (A) of the front oxygen (A/F) sensor.

Fig 1: Identifying Front Oxygen (A/F) Sensor Connector
Courtesy of SUBARU OF AMERICA, INC.
Remove the catalytic converter lower cover. (U5 model)

Fig 2: Locating Catalytic Converter Lower Cover Screws
Courtesy of SUBARU OF AMERICA, INC.
Apply spray-type lubricant to the threaded portion of front oxygen (A/F) sensor, and leave it for one minute or more.
Remove the front oxygen (A/F) sensor.

CAUTION: When removing the front oxygen (A/F) sensor, wait until exhaust pipe cools, otherwise it will damage the exhaust pipe.

Fig 3: Identifying Front Oxygen Sensor RH And LH

Courtesy of SUBARU OF AMERICA, INC.