I've been a tad slow on the uptake over the past couple of days, thanks to a rather crazy weekend (one that went by way too fast). No surprise then, that when I decided to look up Electronic Control Units (ECU) on the web, even the 'dumbed-down' efforts by the patient folks at How Stuff Works and Wikipedia just didn't seem to cut it for me.
That's when I came across this analogy.
In most modern fuel injection systems, there is an electronic control unit. Some car manufactures call it an ECU and other things. Generically we call it the brain, since it does the 'thinking'. Now comparing it to the human body will help you understand how it works. Your brain receives information from your senses - sight, touch, taste, smell and hearing. Using this information the brain tells your body what to do. For example, say your hand touches something hot. Your brain receives this information and decides it's too hot to touch and sends a signal to your hand to pull away. Simple input-processing-output, right?
Now, since a computer doesn't have hands, eyes, ears or noses they need to get relevant information somehow. That's where sensors come in. These sensors are the eyes and ears of the ECU. As the information comes in, the ECU processes it and determines what output to use to do what needs to be done.
Simply put, based on information from various input sensors like the engine coolant temperature, barometric pressure and airflow, the ECU determines optimum settings for the output systems, these being things like the fuel injection, idle speed and ignition timing. What this means for you are things like low emissions and good mileage.
The ECU also interrupts the operation of the air conditioning and controls power to the fuel pump. Most ECUs consist of an 8 or 16-bit microprocessors, random access memory (RAM), read only memory (ROM), and an input/output interface.
More on how fuel injection systems function.