Powertrain Control Module: Notes

Powertrain Control Module (PCM), is located in the left side of the engine compartment, forward of the strut tower, inside the air filter box. See Fig 1.

The PCM maintains 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. To provide optimum driveability and emissions, the PCM monitors input signals from the following components to calculate ignition spark timing:

• The Ignition Control Module (ICM).
• The Throttle Position (TP) sensor.
• The Engine Coolant Temperature (ECT) sensor.
• The Mass Air Flow (MAF) sensor.
• The Intake Air Temperature (IAT) sensor.
• The Vehicle Speed Sensor (VSS).
• The transmission gear position or range information sensors.
• The Engine Knock Sensors (KS)
• A/C clutch control
• Cooling fan control.

The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent driveability and fuel economy. The 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 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 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 MIL. When the PCM detects a malfunction, the PCM stores a DTC. The problem area is identified by the particular DTC that is set.

The PCM 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.

Fig 1: Locating Powertrain Control Module

Courtesy of GENERAL MOTORS CORP.