Camshaft Position Sensor: Description and Operation
Fig. 2 Camshaft Position Sensor -- Inside Distributor (Sync Signal Generator):
PURPOSE
The PCM determines fuel injection synchronization and cylinder identification from inputs provided by the camshaft position sensor and crankshaft position sensor. From the two inputs, the PCM determines crankshaft position.
OPERATION
This vehicle is equipped with a camshaft driven mechanical distributor, containing a shaft driven distributor rotor. The distributor is also equipped with an internal camshaft position (fuel sync) sensor Fig. 2. This sensor provides fuel injection synchronization and cylinder identification to the PCM.
The camshaft position sensor contains a hall effect device called a sync signal generator. This sync signal generator detects a rotating pulse ring (shutter) on the distributor shaft. The pulse ring rotates 180 through the sync signal generator.
Its signal is used in conjunction with the crankshaft position sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders.
When the leading edge of the shutter enters the sync signal generator, the interruption of magnetic field causes the voltage to switch high. This causes a sync signal of approximately 5 volts.
When the trailing edge of the shutter leaves the sync signal generator, the change of magnetic field causes the sync signal voltage to switch low to 0 volts.
Since the shutter rotates at half crankshaft speed, it may take one engine revolution during cranking for the PCM to determine the position of piston number 6.
NO CAM SIGNAL AT PCM FAULT MESSAGE
Purpose
The camshaft position (CMP) sensor is a hall-effect type sensor used to detect the camshaft's position.
Operation
The sensor is provided with 12 volts from the fused ignition switch output circuit and the powertrain control module supplies a sensor ground. The CMP sensor has a 5 volt pull-up from the PCM. The sensor signal is created when the distributor's pulse ring is rotated past the camshaft position sensor.
When Monitored:
The crankshaft position sensor signal trouble code is not set. With the ignition in either the start or run position and battery voltage between 4 and 15 volts.
Set Condition:
Too many crankshaft position sensor signals detected without any camshaft position sensor signal
Possible Causes:
- Open fused ignition switch output circuit (12V)
- Open sensor ground
- Damaged pulse ring
- Failed sensor
- Failed PCM
- Inoperative distributor drive
- Broken timing belt
- Connector terminals
- Connector wires