Engine control unit (ECU), also known as power-train control module (PCM), or engine control module (ECM) is an electronic control unit that controls fuel injection system, spark ignition timing, and the idle speed control system. Modern vehicle ECUs are real-time engine management system computers, designed with microprocessors, sensors/transducers, data acquisition systems, and memories to store software, and CAN bus automotive network to achieve communication between various electronic devices. Modern ECU may also control the engine cooling fans, cruise control, transmission control, anti-skid brake control, and anti-theft control, and HVAC Compressor.

Duties of Engine Control Unit (ECU)

  • ECU controls fuel mixture during fuel injection according to how much air is passing into the engine when throttle pedal is pressed. Fuel mixture control on computer controlled carburetors works similarly
  • ECU controls spark ignition timing to initiate combustion in the combustion chamber. ECU can adjust the exact timing of the spark ignition timing to provide better power and economy.
  • ECU controls the idle speed of engine to anticipate the engine load at idle. Most engine systems have idle speed control built into the ECU. Changes in this idle load may come from HVAC systems, power steering systems, power brake systems, and electrical charging and supply systems
  • ECU also controls variable valve timing to optimize the flow of air into the cylinder, increasing power and economy.

Programmable Engine Control Modules (ECM)

Programmable engine control modules (ECM) are required where significant aftermarket modifications have been made to a vehicle’s engine. Examples include adding or changing of a turbocharger, adding or changing of an intercooler, changing of the exhaust system, and conversion to run on alternative fuel. As a consequence of these changes, the old ECU may not provide appropriate control for the new configuration. In these situations, a programmable ECU can be wired in. These can be programmed/mapped with a laptop connected using a serial or USB cable, while the engine is running.

Modern Engine Management System (EMS)

Modern Engine Management Systems (EMS) use a microprocessor which can process the inputs from the engine sensors in real time. An electronic control unit contains the hardware and software (firmware). The hardware consists of microcontroller chip (CPU), sensors/transducers, data acquisition systems, and memories to store software. Also Engine Management System (EMS) is usually developed with Controller Area Network or CAN bus automotive network to achieve communication between various electronic devices.

Modern ECU computers may also control the engine cooling fans, cruise control, transmission control, anti-skid brake control, and anti-theft control, and HVAC Compressor, etc.