ECM Function

The ECM can supply 5 volts or 12 volts to the various sensors or switches. This is done through pull-up resistors to the regulated power supplies within the ECM. In some cases, even an ordinary shop voltmeter will not give an accurate reading because the resistance is too low. Therefore, a DMM with at least 10 megohms input impedance is required in order to ensure accurate voltage readings.

The ECM controls the output circuits such as the injectors, the relays, the IAC, etc. by controlling the ground or the power feed circuit through the transistors or a device called an output driver module.