ECM Function

The engine control module (ECM) can supply 5 volts, 12 volts, or ground to various sensors or switches. Voltage is supplied through pull-up resistors to the regulated power supplies within the ECM. In some cases an ordinary shop voltmeter will not give an accurate reading due to low input resistance. A DMM with at least 10 megaohms input impedance is required in order to ensure accurate voltage readings.

The ECM controls the output circuits by controlling the ground or the power feed circuit through the transistors or a device called an output driver module.