Powertrain Control Module

Powertrain Control Module

The powertrain control module (PCM) is located in the engine compartment. The PCM is the control center of the vehicle.

The PCM constantly monitors the information from various sensors, and controls the systems that affect vehicle performance and the emissions. The PCM also performs the diagnostic functions for those systems. The PCM can recognize operational problems and will alert the driver through the Malfunction Indicator Lamp (MIL) when a malfunction occurs. When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC), which will help to identify the problem areas. This process helps the technician in making repairs.

The PCM supplies either 5 volts or 12 volts in order to power the various sensors or switches. This is done through resistances in the PCM. The resistance is so high in value that a test lamp will not illuminate when the lamp is connected to the circuit. In some instances, even an ordinary shop voltmeter will not give an accurate reading because the resistance is too low. Therefore, a digital voltmeter (DMM) with a minimum of 10 megaohms input impedance is required in order to ensure accurate voltage readings.

The PCM controls output circuits such as the injectors, the IAC, and the cooling fan relays by controlling the ground or the power feed circuit through transistors or with an output driver module.


The PCM controls all ignition system functions, and constantly corrects the basic spark timing. The PCM monitors information from various sensor inputs that include the following:

- The throttle position (TP) sensor

- The engine coolant temperature (ECT) sensor

- The mass airflow (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)