What does a car’s computer do? Does it receive input from the car’s mechanical components? And if so, how?


What does a car’s computer do? Does it receive input from the car’s mechanical components? And if so, how?

In: Technology

Most operations in a modern car have at least one aspect affected or controlled by the cars computer. A major function is keeping the engine running well by making adjustments to the timing of things like the fuel injectors and spark plugs. They also help with emissions with info received from things like the O2 sensor, air pressure and temperature sensors, engine temperature sensor, and throttle position. Another major role is diagnostics if anything goes wrong. It’s in charge of the check engine light, which is really just a signal that an error code has occurred. These problems can be as simple as low washer fluid or signs of much more complex problems.

The cars computer keeps track of data from various sensors throughout the car.

For example there’s a crank shaft position sensor that tracks the rotation of the crank shaft.

Oxygen sensors in the exhaust to measure how much Oxygen is left after combustion.

Fuel flow sensors to know how much fuel you are burning.

Temperature sensors to measure air temperature and the temp of the engine.


It uses this data to manage your engine, changing fuel flow and conditions within the engine to optimize its performance based on pre-programmed settings. Most engines are tuned by the manufacturer to maximize the life time of the engine and overall efficiency. Changing some settings in the computer can significantly boost performance at the price of efficiency and extra wear, although this isn’t recommended.

The most important thing it does is regulate the timing of every part of the car(such as the combustion cycle in the engine) to be more precise than an analog counterpart, and thus increase fuel efficiency. Other than that, it receives general diagnostic input from the car’s components, like low oil level, or something wrong with the engine. All new cars are completely wired up.

Each sensor in the car reads something like fuel level or rpm of the engine, but just many, many more sensors. Each one returns a digital (on or off) or analog (a voltage range from 0-12V) and the cars many computers process those inputs. Other parts are controlled by the computer and are either turned on or off (digital) or controlled with variable voltage (analog).
This is oversimplified but mechanical components are controlled with actuators (motorized levers) or solenoids (electromagnetic push/pull).

The cars engine control unit (ECU) will have several sensor inputs, such as throttle position, oxygen sensor, exhaust gas sensor, camshaft sensor, coolant temp sensor.

Input -> Calculation -> Output

The ECU will then have software stored within it to calculate how much fuel and air to add into the engine. This varies with the sensor inputs and situations. Obviously you don’t need much fuel or air when parked up and idling.

This software is called the engine map. The map can be changed for better fuel economy or performance (the only difference between my car and its more expensive faster version is only the ECU map and exhaust pipe!)

The ECU then outputs / controls the fuel injectors, spark plugs and throttle body (amount of air going into the engine). In some cars the ECU can change the valve timing (VTEC)