LH side

Before installing front oxygen sensor, apply anti-seize compound only to the threaded portion of front oxygen sensor to make the next removal easier.
Anti-seize compound:

SS-30 JET LUBE

CAUTION: Never apply anti-seize compound to the protector of front oxygen sensor.
Install the front oxygen sensor.
Tightening torque:

21 N.m (2.1 kgf-m, 15.2 ft-lb)

Fig 1: Installing Front Oxygen Sensor
Courtesy of SUBARU OF AMERICA, INC.
Hold the front oxygen sensor harness with clip.

Fig 2: Holding Front Oxygen Sensor Harness With Clip
Courtesy of SUBARU OF AMERICA, INC.
Lower the vehicle.
Connect the connector of front oxygen sensor.

Fig 3: Connecting Connector Of Front Oxygen Sensor
Courtesy of SUBARU OF AMERICA, INC.
Connect the battery ground cable to battery.

Fig 4: Connecting Battery Ground Cable To Battery
Courtesy of SUBARU OF AMERICA, INC.