The PCM/ECM receives data from a number of sensors and other electronic components (switches, relay, etc.). Based on information received and information programmed in the PCM/ECM's memory, it generates output signals to control various relay, solenoids and other actuators. The PCM/ECM in this system has calibration modules located inside the assembly that contain calibration specifications for optimizing emissions, fuel economy and driveability. The calibration module is called a PROM.
The following are the electronic engine controls used by Mazda trucks (note that not all of these sensors may be found on one engine):
Because of the complicated nature of this system, special tools and procedures are necessary for testing and troubleshooting.