Control Units

The heart of any computer system is the control unit, or control module. These computers are usually sealed in a metal box and are linked to the system by a wiring harness with multi-pin connector. The computers are usually located in the passenger compartment for protection from moisture, vibration and temperature extremes.

The job of the computer is to coordinate vehicle operation and equipment. When engineers develop the systems, they simulate every conceivable driving condition and determine the best adjustments for economy, driveability and low emissions. These selected adjustments are in the computer's program and are used by the vehicle at certain times.

Systems are said to operate in either "Open Loop" or "Closed Loop". In an open loop condition, the instructions and decisions made by the designers are used to run the engine. The computer just follows their orders. In closed loop, the computer reads the values from a number of sensors and makes tuning decisions based on past experience and present conditions. This ability makes the system more responsive, and allows the computer to compensate for unusual or severe driving conditions.