The EEC-IV system uses a microprocessor to receive and process information from a number of sensors and other electronic components. The processor contains a specific calibration for maintaining optimum emissions, fuel economy and driveability. By comparing the input signals to its own calibrated program, the processor generates output signals to the various relays solenoids and actuators through the engine compartment.
The EEC-IV processor, located under the instrument panel, to the left of the steering column, communicates service information to the outside world by way of the "Self-Test'' service codes. These codes are two-digit numbers signaling that an input has been received which is not within the parameters of the computer program. When the EEC-IV module receives an input telling it that a system is malfunctioning, it alerts the driver by turning on the "Check Engine'' light in the instrument panel. If equipped with the proper tools, the driver can retrieve the necessary information from the EEC-IV module, or take the vehicle to an individual who has the proper equipment to retrieve the data.