Powertrain Control Module: Notes

NOTE: Powertrain Control Module (PCM) may also be referred to as Electronic Control Module (ECM) or Vehicle Control Module (VCM). PCM is located either in front of shifter below center console, or on fenderwell in engine compartment.

The PCM supplies either 5 or 12 volts to power various sensors or switches. The power is supplied through resistances in the PCM which are so high in value that a test light will not light when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. Therefore, a digital voltmeter with at least 10 megohms input impedance is required to endure accurate voltage readings. Tool (J 39200) meets this requirement. The PCM controls output circuits such as the injectors, fan relays, etc., by controlling the ground or the power feed circuit through transistors or through either the Output Driver Module (ODM), or the Quad Driver Module (QDM). The input/output devices in the PCM include an analog-to-dial converters, signal buffers, counters, and special drivers. The PCM controls most components with electronic switches which complete a ground circuit when turned "ON". These switches are arranged in groups of 4 and 7, called either a surface-mounted Quad Driver Module (QDM), which can independently control up to 4 output terminals, or QDMs which can independently control up to 7 outputs. Not all outputs are always used.

The PCM is designed to maintain exhaust emission levels to government mandated standards while providing excellent driveability and fuel efficiency. The PCM monitors numerous engine and vehicle functions via electronic sensors such as the Throttle Position (TP) sensor, Heated Oxygen (HO2S) sensor, and Vehicle Speed Sensor (VSS). The PCM also controls certain engine operations through the fuel injector control, ignition control module, ION sensing module, automatic transmission shift functions, cruise control, evaporative emission purge, A/C clutch control.