Camshaft Position Sensor

The camshaft position sensor is located on the cylinder head. It detects the combustion cylinder at any given moment.
The sensor generates a pulse when one of the slots in the camshaft plate passes in front of the sensor. The ECM detects the camshaft position by measuring the pulse.
Three slots are provided on the plate as shown below.

Fig 1: Identifying Camshaft Plate, Slot And One Rotation Waveform
Courtesy of SUBARU OF AMERICA, INC.