Secondary Speed Sensor: Inspection

Remove the bulkhead harness connector from TCM. Ref. to REMOVAL , Transmission Control Module (TCM).
Set the ST between the TCM and bulkhead harness.
ST 18460AA040 CHECK BOARD
Set the probe of oscilloscope to the check board connector.
Terminals:

No. 13 (+) - No. 26 (-)

Fig 1: Bulkhead Harness Connector Terminals
Courtesy of SUBARU OF AMERICA, INC.
Start and warm up the engine.
Check the waveform of secondary speed sensor with engine idling.

NOTE: The waveform cycle changes as the speed changes.

Fig 2: Secondary Speed Sensor Waveform

Courtesy of SUBARU OF AMERICA, INC.