from the subaru manual (02 wrx):
Quote:
1 . DESCRIPTION
9 The speedometer system is an electrical type that uses electric signals from the speed sensor
in the MT model or the transmission control module (TCM) in the AT model .
The vehicle speed sensor is installed on the manual transmission .
Since the system does not use mechanical components such as rotating cable, there are no
opportunities of occurring such problems as meter needle vibration and cable disconnection .
Also, it does not constitute any means of mechanical noise transmission .
The odometer and tripmeter readings appear on a liquid crystal display (LCD) .
. OPERATION
MT model : The vehicle speed sensor sends vehicle speed signals (4 pulses per rotation of speed
sensor's driven shaft) to the speedometer drive circuit and odometer/tripmeter drive circuit in the
speedometer,
AT model : The TCM sends vehicle speed signals (4 pulses per rotation of output shaft) to the
speedometer drive circuit and odometer/tri p meter drive circuit in the speedometer.
NOTE :
Signals from the speed sensor or TCM are also used by the engine control module, automatic
transmission control module, etc.
