Firebird V8-350 5.7L VIN P SFI (1996)
Camshaft Position Sensor: Description and Operation
The distributor contains a signal disk and two optical camshaft position (CMP) sensors that provide signals to the PCM for timing control. One CMP
sensor senses 360 equally-spaced slots in the signal disk to provide 720 signals per camshaft revolution for high-resolution timing control. The other
CMP sensor senses 8 disk slots of variable length, providing a low-resolution signal that tells the PCM which spark plug is being fifed. Power for the
optical CMP sensors, a system ground, and the two CMP sensor signals are transferred between the PCM and the distributor through a shielded harness
connected to the four-terminal connector on the distributor.
The ignition system supplies two timing inputs to the PCM, a high resolution signal (360 pulses per one camshaft revolution) and a low resolution signal
(8 pulses per one camshaft revolution). The PCM can determine if one of the timing inputs is not being received by comparing the two inputs. If the
PCM detects one timing pulse without detecting the other timing pulse, diagnostic trouble code 16 or 36 will set.
The reference signals toggle between 0 and 5 volts as the camshaft turns. Therefore, an open, a short to voltage, a short to ground, or a defective sensor
inside the distributor can prevent the voltage from pulsing at the PCM.
The ignition coil/ignition control module provides spark to the distributor, timed by signals from the PCM. Power (B+) for the ignition coil primary
circuit and the ignition control module is supplied by the ignition switch. The PCM combines the camshaft position information supplied by the
distributor with other system parameters and calculates the required spark advance and coil dwell. The PCM signals the ignition control module, which
turns on the primary
current to the ignition coil by grounding the primary circuit, and then turns it off by removing the ground. when the primary current flow stops, high
voltage induced in the ignition coil secondary winding becomes the spark voltage for the spark plug. The spark voltage is delivered to the distributor
through the coil output (secondary) wire, and then directed to the proper spark plug connector by the distributor rotor.
