Subaru 2002 Impreza Service Manual page 38

SENSORS AND SWITCHES
Fuel Injection (Fuel
System)
E: CAMSHAFT POSITION SENSOR
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The camshaft position sensor is located on the left-hand camshaft support. It detects the com-
bustion cylinder at any given moment.
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The sensor generates a pulse when one of the bosses on the back of the left-hand camshaft
drive sprocket passes in front of the sensor. The ECM determines the camshaft angular position
by counting the number of pulses.
Internal construction and the basic operating principle of the camshaft position sensor are similar
to those of the crankshaft position sensor. A total of seven bosses are arranged at equally spaced
four locations (one each at two locations, two at one location, and three at one location) of the
sprocket as shown below.
(1) Boss
(2) Camshaft sprocket
(3) Airgap
S2H1813A
(4) Camshaft position sensor
(5) Boss
(6) Camshaft one rotation (Crankshaft two rotations)
FU-22