Knock Sensor: Removal

Remove the collector cover.
Disconnect the ground cable from the battery

Fig 1: Disconnecting Ground Cable From Battery
Courtesy of SUBARU OF AMERICA, INC.
Remove the intake manifold. < Ref. to REMOVAL , Intake Manifold. >
Disconnect the knock sensor connector.
Remove the knock sensor from the cylinder block.

Fig 2: Identifying Knock Sensor
Courtesy of SUBARU OF AMERICA, INC.