Gasoline Models

The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent driveability and fuel economy. The Powertrain Control Module (PCM) is the control center of this system. The PCM controls the air/fuel metering system to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop the PCM adds oxygen sensor inputs to calculate short and long term fuel trim fuel delivery adjustments. Short Term fuel trim values change rapidly in response to the Heated Oxygen Sensor (HO2S) voltage signals. Long Term FT values change slower in response to trends in Short Term FT adjustments. Fuel Trim Index is the average of Short and Long Term Fuel Trim and Purge Learn Memory based on engine speed and load.

The PCM also performs the diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the Malfunction Indicator Light (MIL). When the PCM detects a malfunction, the PCM stores a Diagnostic Trouble Code (DTC). The problem area is identified by the particular DTC that is set. The PCM supplies a buffered voltage to various sensors and switches. Review the components and wiring diagrams to determine which systems are controlled by the PCM. The following are some of the functions that the PCM controls:

• The engine fueling.
• The Ignition Control (IC).
• The Knock Sensor (KS) system.
• The Evaporative Emissions (EVAP) system.
• The secondary Air Injection (AIR) system (if equipped).
• The Exhaust Gas Recirculation (EGR) system.
• The automatic transmission functions.
• The generator.
• The A/C clutch control.
• The cooling fan control.

The input and output devices in the PCM include analog-to-digital converters, signal buffers, counters, and output drivers. The output drivers are electronic switches that complete a ground or voltage circuit when turned on. Most PCM controlled components are operated via output drivers. The PCM monitors these driver circuits for proper operation and, in most cases, can set a DTC corresponding to the controlled device if a problem is detected.