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An engine control unit (ECU), also called an engine control module (ECM), [1] is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems.
The development of an ECU involves both hardware and software required to perform the functions expected from that particular module. Automotive ECU's are being developed following the V-model. [ 1 ] Recently the trend is to dedicate a significant amount of time and effort to develop safe modules by following standards like ISO 26262 . [ 5 ]
Over the years, there were many variations of EEC-IV modules depending on the number of engine cylinders and the types and quantities of inputs and outputs. There were even a series of special EEC-IV modules designed for use in Formula 1 race cars, making Ford one of the earliest adopters of digital electronics on a race car.
The ECM is a type of electronic control unit (ECU), which is an embedded system that employs software to determine the required throttle position by calculations from data measured by other sensors, including the accelerator pedal position sensors, engine speed sensor, vehicle speed sensor, and cruise control switches.
The BCM communicates with other on-board computers via the car's CAN bus system, and its main application is controlling load drivers – actuating relays that in turn perform actions in the vehicle such as locking the doors, flashing the turn signals (in older cars), or dimming the interior lighting.
On some cars, such as many Chryslers, there are multiple computers: the PCM, the TCU, and the Body Control Module (BCM), for a total of three separate computers. These automotive computers are generally very reliable. The PCM commonly controls more than 100 factors in a car or truck.
The typical modern TCU uses signals from engine sensors, automatic transmission sensors and from other electronic controllers to determine when and how to shift. [2] More modern designs share inputs or obtain information from an input to the ECU, whereas older designs often have their own dedicated inputs and sensors on the engine components.
The road speed function can be used to evaluate vehicle speed and possibly activate a speed limiter (Heavy Vehicles), or maintain or restore a set speed (cruise control). Further functions can include exhaust brake operation which, when activated, will result in the fuel pump rack position being set to zero delivery or idle.