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 Oscilloscope Positive And Negative Probes
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 With Engine Idling Waveform
Courtesy of SUBARU OF AMERICA, INC.