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Engine Control

Basic Description

The average new car has dozens of computers that control everything from the airbags and brakes to the lights and entertainment system. However, when someone refers to "the car's computer," they are probably referring to the engine control module (ECM). The ECM generally employs the most powerful (and expensive) microcontroller in the vehicle. Engine control modules determine where to set the throttle, how much fuel to inject into the cylinders, and when to fire the spark plugs. In many vehicles this controller also regulates the electric power distribution, provides the on-board diagnostics, and communicates with a number of other automotive systems to share information it obtains from various sensors.

Engine control modules take data from a wide variety of analog sensors, digitize this information, and use it to calculate the proper engine settings. The results of these calculations are converted to actuator settings, and both digital and analog outputs from the module are used to operate these actuators. The diagram below illustrates some of the primary sensors and actuators employed by the engine control module.

Schematic view

Although cars did not have engine control modules for the first 80 - 90 years after the gasoline engine was invented, cars today would not be able to meet modern fuel efficiency and emissions requirements without them. Improvements in engine control algorithms, data collection, and data communication continue to be a major reason that cars are more efficient and less polluting with each new model year.

Some vehicles allow the driver to make trade-offs between power and fuel economy by simply activating a switch that causes the ECM to run different engine control subroutines. There are also various programmable ECMs that are available to give car enthusiasts a great deal of control over how their engine will perform in various situations.

Today's ECMs generally employ 32-bit microcontrollers with a few megabytes of memory clocked at speeds between 32 MHz and 100 MHz. They generally communicate with other electronic modules using one or more CAN bus interfaces. In cases where the engine control function and the transmission control function are combined in the same module, the module is generally referred to as a powertrain control module (PCM).

Pedal position sensor, throttle valve position sensor, engine oil temperature sensor, oxygen sensor, induction air temperature sensor, EGR sensor, oil pressure sensor, fuel level sensor, wheel speed sensor, torque sensor, knock sensor, air flow sensor, crankshaft position sensor, camshaft position sensor, manifold absolute pressure sensor, coolant temperature sensor
Fuel injectors, spark plugs, EGR valve, fuel tank venting, cooling fan, starter motor, throttle position motor, check engine light
Data Communications
CAN Bus (FlexRay and/or LIN bus communications may also be employed)
ACDelco, AEM, AFS, Bosch, Cardone, Continental, Delphi, Denso, EControls, Electromotive, Fujitsu Ten, Haltech, Hitachi, Holley, Hyundai Kefico, Keihin, LifeRacing, Magneti Marelli, Mitsubishi Electric, Motec, Performance Electronics, Pi Innovo, Steyr, Visteon, Woodward, Westport
For More Information
[1] Engine Control Unit, Wikipedia.
[2] How the Engine Control Module Works, Cherise LaPine,, May 8, 2012.
[3] Computer PCM, Ken Lavacot,, Aug. 24, 2009.
[4] ECU Explained,
[5] ECM/PCM Replacement, YouTube, Aug. 13, 2010.
[6] ECU Electronic Control Unit, YouTube, Sep. 1, 2011.
[7] Engine Control Module (ECU) Ground Circuit, YouTube, Jan. 24, 2012.
[8] Arduino Engine Control Unit, YouTube, Aug. 4, 2013.