ECM/PCM is activated by power supply. Signals from several sensors, such as CKPS and APS, is inputted to ECM/PCM. Comparing inputted signals with control LOGIC saved at micro controller and EEPROM, ECM controlls engine as actuating injectors, solenoids and relays.

To guarantee accurate control, ECM/PCM performs SELF TEST, DIAGNOSIS of several sensors and actuators. And if serious trouble which affects vehicle performance occurrs, ECM/PCM sets DTCs.

At certain cases, ECM/PCM shuts down whole systems in order to prevent dangerous situation due to incorrect control.