Knock Sensor: Removal

Disconnect the ground cable from battery.
Remove the clip (A) from the air intake boot.
Loosen the clamp (B) securing the air cleaner case (rear) to the air intake boot.
Loosen the clamp (C) which secures the throttle body to the air intake boot.

Fig 1: Identifying Throttle Body And Air Intake Boot Clamp
Courtesy of SUBARU OF AMERICA, INC.
Remove the air intake boot from the throttle body, and move it to the left side wheel apron.

Fig 2: Identifying Air Intake Boot And Throttle Body
Courtesy of SUBARU OF AMERICA, INC.
Disconnect the connector (A) from the knock sensor, and remove the knock sensor from the cylinder block.

Fig 3: Locating Knock Sensor Connector
Courtesy of SUBARU OF AMERICA, INC.