Powertrain Control Module (PCM)

Powertrain Control Module (PCM):

The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. Ignition Control (IC) spark timing is the method the PCM uses to control spark advance and ignition dwell. To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC) spark timing:
^ Ignition Control (IC) module
^ Engine Coolant Temperature (ECT) sensor
^ Intake Air Temperature (IAT) sensor
^ Mass Air Flow (MAF) sensor
^ Internal Mode or PNP inputs from Internal Mode switch or Park/Neutral position switch
^ Throttle Position (TP) sensor
^ Vehicle Speed (VSS), or Transmission Output Speed (TOSS) sensor

The following describes the PCM to IC module circuits:
^ Low resolution engine speed -PCM input - From the ignition control module, the PCM uses this signal to calculate engine RPM and crankshaft position. The PCM also uses the pulses on this circuit to initiate injector operation.
^ Low reference - PCM input - This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the IC module. This circuit assures there is no ground drop between the PCM and IC module.
^ IC timing signal -PCM output - The IC module controls spark timing while the engine is cranking, this is called bypass mode. Once the PCM receives low resolution engine speed signals from the IC module, the PCM applies 5 volts to the IC timing signal circuit allowing the IC module to switch spark control to PCM control.
^ IC timing control- PCM output - The IC output circuitry of the PCM sends out timing signals to the IC module on this circuit. When in the Bypass Mode, the IC module grounds these signals. When in the IC Mode, the signals are sent to the IC module to control coil dwell and spark timing. Proper sequencing of the ignition coils is always controlled by the IC module.