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: Identifying Check Board 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 Signal Waveform
Courtesy of SUBARU OF AMERICA, INC.