Powertrain Control Module/Engine Control Module

The powertrain control module (PCM)/engine control module (ECM), located inside passenger kick-panel, is control center of fuel injection system. It constantly looks at information from various sensors and controls systems that affect vehicle's performance. The PCM/ECM also performs diagnostic functions of system. It can recognize operational problems, alert driver through Malfunction Indicator Lamp (MIL), and store diagnostic trouble code(s) which identify problem areas to aid technician in making repairs.

There are no serviceable parts in PCM/ECM. The calibrations are stored in PCM/ECM in Programmable Read-Only Memory (PROM).

The PCM/ECM supplies either 5 or 12 volts to power sensors or switches. This is done through resistances in PCM/ECM which are so high in value that a test light will not come on when connected to circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. You must use a digital voltmeter with a 10 megohm input impedance to get accurate voltage readings. The PCM/ECM controls output circuits such as fuel injectors, idle air control valve, A/C clutch relay, etc., by controlling ground circuit through transistors or a device called a "quad-driver".