PCM Timing Mode

Position Sensor Signals:

The Powertrain Control Module (PCM) controls spark advance and fuel injection for all driving conditions. The PCM monitors input signals from the following components as part of its ignition control function to determine the required ignition timing:
^ Ignition Control Module (IC Module).
^ Engine Coolant Temperature (ECT) sensor.
^ Manifold Absolute Pressure (MAP) sensor.
^ Transaxle Range (TR) switch.
^ Throttle Position (TP) sensor.
^ Vehicle Speed Sensor (VSS).
^ Knock Sensor (KS).
^ The Crankshaft Reluctor Ring has 24 evenly spaced notches plus 8 additional notches (shaded) used for synchronization.
^ As the crankshaft rotates, the notches pass the position sensors and create a voltage pulse signal in the sensor that is an input for the ignition control (IC) module.
^ Because of the physical location of the 2 crankshaft position sensors, the signal of "B" lags the signal of "A" by 27 degrees of crankshaft revolution.
^ To synchronize the ignition, the IC module first counts the number of "B" pulses between every 2 "A" pulses. There can be 0, 1 or 2 "B" pulses between "A" pulses.
^ When the IC module sees 0 "B" pulses between "A" pulses, it starts counting "B" pulses between "A" pulses. When the IC module counts exactly 4, it synchronizes the ignition on the very next "A" pulse. If the IC module counts over 4 (jumps from 3 to 5), it waits for another "B" pulse between "A" pulse to start counting again.
^ This process allows the ignition to synchronize and fire the first spark plug within 180 degrees (1/2 engine revolution).
^ The camshaft position sensor provides the IC module with cylinder #1 firing order information, which the PCM uses for sequential fuel injection.
^ Using 3 sensors allows the IC module to maintain ignition synchronization even if one of the 3 sensors fails.