Turbine Speed Sensor: Inspection

Remove the instrument panel lower cover. Refer to REMOVAL .
Set the probe of oscilloscope to TCM harness connector.
Connector & terminal

(B54) No. 20 (+) - No. 1 (-):

Fig 1: TCM Harness Connector Terminal Identification
Courtesy of SUBARU OF AMERICA, INC.
Start and warm up the engine.
Check the waveform and output voltage of the turbine speed sensor with engine idling.

Fig 2: Turbine Speed Sensor Output Voltage Waveform
Courtesy of SUBARU OF AMERICA, INC.