Electronic Control Unit - ECU

The Brains of the Vehicle

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Ciulla, Vincent. "Electronic Control Unit - ECU." ThoughtCo, Sep. 2, 2016, thoughtco.com/electronic-control-unit-ecu-4083663. Ciulla, Vincent. (2016, September 2). Electronic Control Unit - ECU. Retrieved from https://www.thoughtco.com/electronic-control-unit-ecu-4083663 Ciulla, Vincent. "Electronic Control Unit - ECU." ThoughtCo. https://www.thoughtco.com/electronic-control-unit-ecu-4083663 (accessed October 22, 2017).

The Electronic Control Unit (ECU) is a general term for any of a number of computer modules that receive input from sensors in your automobile and control different electrical functions. They are the computer brains of your vehicle. As autos become more complex and outfitted with more sensors and functions, there can be dozens of different ECUs at work in a single vehicle.

Some common ECUs include the Engine Control Module (ECM), Powertrain Control Module (PCM), Brake Control Module (BCM), General Electric Module (GEM).

 The ECU often consists of an 8-bit microprocessor, random access memory (RAM), read only memory (ROM), and an input/output interface. They look a lot like a computer hard drive.

ECUs may be upgraded by the manufacturer or by a third party. They are usually protected to prevent unwanted tampering.

Fuel Management by the Engine Control Module (ECM)

One typical ECU is the Engine Control Module (ECM), which controls the fuel injection system, ignition timing, and the idle speed control system of an automobile. The ECM also interrupts the operation of the air conditioning and EGR systems, and controls power to the fuel pump (through the control relay).

Based on information from the input sensors (engine coolant temperature, barometric pressure, air flow, etc.), the ECU determines optimum settings for the output actuators (injection, idle speed, ignition timing, etc.).

Fuel management is one of the main functions of the ECU.

The computer determines how long the injectors stay open, which controls the amount of fuel used. This is only from four to nine milliseconds, done 600 to 3000 times per minute.  The computer controls how much voltage is sent to the fuel pump, raising and lowering fuel pressure. The ECU also controls engine timing, which is when the spark plugs fire.

Electronic Control Unit and Safety

With modern safety equipment, the electronic control unit (ECU) is the brains of the air bag system. It gets signals from crash sensors and processes this data to decide which, if any, air bags should be triggered. In advanced air bag systems, there may be sensors that detect the weight of the occupants, where they are seated, and whether they are using a seatbelt. All of these factors help it to decide whether to deploy the frontal air bags. The ECU does regular diagnostic checks and lights a warning light if anything is amiss.

The ECU is usually positioned in the middle of the vehicle, or it may be under the front seat. This position protects it, especially during a crash when it is most needed.

Related Resources:

There are a lot of things going on in your engine as you drive. Information is taken in from the sensors and processed. But how is this information gathered and what happens to it once it's collected?

More about how sensors work in your automobile. How the data from the sensors is processed and converted into action.