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 monitors numerous engine and vehicle functions. The PCM constantly looks at the information from various sensors and other inputs, and controls the systems that affect vehicle performance and emissions. 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 lamp (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 control module supplies a buffered voltage to various sensors and switches. Review the components and wiring diagrams in order 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

4.2 L in-line 6 cylinder engine sensor locations.
4.2L Engine Computer (PCM) Description

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Powertrain Control Module Function
The powertrain control module (PCM) constantly looks at the information from various sensors and other inputs and controls systems that affect vehicle performance and emissions. The PCM also performs diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the malfunction indicator lamp (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 control module supplies a buffered voltage to various sensors and switches. 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.