It's definitely safe to say that our cars have come a long way since the late 1800s. The modern car is jam-packed with technology unimaginable in the past, and it's all because of one very important part: the ECU.

Thanks to the ECU or electronic control unit (more commonly known as the computer box), the car of today is far safer and more efficient than it ever was. Simply put, the ECU is the brain of the automobile as it ensures the vehicle operates optimally at all times.

So what does the computer box or ECU compute or manage? Read on and see how a simple box is responsible for almost everything that your car does.

Automotive 101: What exactly does the computer box in your car compute?

The Carburetor: The All-Mechanical Age

Before discussing computer boxes, we shall take a step back to a time when computers would still take up a whole building or office; a time when cars were said to be 'all mechanical'. During this era, automobiles did not have things like electronic fuel injection or sensors; drivers back then relied on a good mechanic with a few wrenches and screwdrivers to get the car running smoothly.

Automotive 101: What exactly does the computer box in your car compute?

Instead of fuel injection or direct injection which are commonly found in cars nowadays, engines used to have carburetors in order to fine tune the air-fuel mixture. A distributor was still used to control spark timing rather than coil packs, ensuring proper spark distribution among all cylinders. No computer or electronics would be controling any of these features. Even the fuel pressure wasn't that high; today's EFI systems use high pressures to fully "mist" the fuel for better combustion, but that wasn't the case for carburetor engines. 

It wasn't just the engine that was all mechanical. Other vehicle functions relied on vacuum hoses, solenoids and basic electrical contacts to make things work like the the retard when you lift off the throttle, or the idling for your airconditioning system. While modern vehicle electronics sound complicated, wires were less cumbersome than vacuum hoses and hydraulic lines.

Automotive 101: What exactly does the computer box in your car compute?

EFI: The Rise of Computer-controlled Engines

An engine equipped with a carburetor needed a good, qualified mechanic who can fine tune it to run at optimum levels. Mechanics of the day typically needed a screwdriver and good senses to tell if the engine is running rich, lean, or just right.

An EFI system did away with not only the carburetor, but the mechanic as well. There was no need for a carburetor as its duties were taken over by the throttle body with the traditional "butterfly valve" as well as one high-pressure fuel injector per cylinder. There was also no need for a mechanic to manually adjust the carburetor as the the ECU would take readings from a variety of sensors, particularly the air flow sensor and the oxygen sensor to learn what the car is doing and adjust the fuel accordingly. 

One of the manufacturers first credited for using a computer box so was Volkswagen, back in 1968. They system was manufactured by Bosch replaced the carburetor system with an electronic fuel injection (EFI) system.

Automotive 101: What exactly does the computer box in your car compute?

When the computer box was first introduced it monitored only a few engine parameters and mainly controlled fuel injection and in turn the air-fuel mixture; the crucial ratio of air and gasoline or diesel that the engine needed to get going.

Limitations of technology at the time prevented it from being complex as well; despite having ECUs, some most of the engines at the time still combined some analog features of the day such as the distributor in order to run.

In the late 70s, ECUs were becoming more and more prevalent on most vehicles due to emissions regulations becoming ever more stringent. By the 1980s, more manufacturers began using ECUs and EFI systems on their vehicles as carburetors were found to be less reliable than fuel injection. As the years went by, the computers and chips became  smaller and more capable. This allowed for more advanced engine monitoring such as the closed-loop system.

Essentially, a closed-loop system uses a mass airflow (MAF) sensor (shown above) positioned at the intake, and oxygen sensors positioned at the exhaust/headers to adjust the air-fuel ratio accordingly. The O2 sensor sends a particular voltage to the ECU to indicate if it is running rich (too much fuel), running lean (too much air), or stoich (just right). That information is fed to the ECU which then controls how much fuel is squirted into the engine from the injectors. 

This was the key goal of EFI: ensuring that the engine gets the right amount of fuel after reading the sensors within the closed-loop system. 

Automotive 101: What exactly does the computer box in your car compute?

Safety gets an electronic aid

It's not just the engine that got a big helping from the electronic control unit. For example, anti-lock braking systems (ABS) used to rely on vacuum hoses but with the trickle-down effect of technology, ABS eventually became electronically-controlled. The modern ABS has sensors on each wheel which then sends to the ECU to override the brakes to prevent a lock-up that could deprive the driver of steering control in emergency maneuvers.

Automotive 101: What exactly does the computer box in your car compute?

Another safety feature that relies on the ECU is the traction control system (TCS). Like ABS, there are also wheel sensors that send information to the ECU, but instead of controlling the brakes, the 'brain' will tell the engine to cut power to regain grip. Kicking it up a notch is electronic stability control (ESC), a system wherein the ECU continuously scans the car's sensors and activates when it senses that loss of control is imminent. The electronics take over the brakes and engine to allow the car to stay on its intended path.

Thanks to advances in technology, ECUs can now also handle more complex features such as autonomous emergency braking, adaptive cruise control and so much more. While modern safety systems level up a vehicle's overall safety, the role of the ECU remains the same: monitoring sensors and adjusting the relevant system accordingly. 

Automotive 101: What exactly does the computer box in your car compute?

Computers everywhere

Together with the rise of technology, ECUs of vehicles became ever more complex as well. Not only did they handle the fuel mixture and timing, they also controlled other electrical processes of the vehicle as well. Sensors were now installed all over the vehicle and allowed for better monitoring of the system. The rise of OBD system improved on that even more. Using an OBD scanner, one could locate the errors sent by the ECU which is displayed on the dash.

At the same time, ECUs also came to be programmable, particularly in the aftermarket scene. This led to most racers installing them on their vehicles in order to maximize output without the need to change parts. Peak engine performance could be extracted simply from a tune of the car's computer combined with simple aftermarket supporting modifications. Aftermarket ECUs can be found from multiple manufactures and can either 'piggyback' on your factory ECU or replace it completely.

What does the computer box in your car compute 

Nowadays, computers control and monitor everything. The once simple computer box which controlled ignition and fuel now also controls a plethora of systems and reads many kinds of sensors as well. In fact some systems have their own separate computers and control units, all of which work together to make a modern car run properly. The downside is that the ECU and the presence of more electronics have potentially made cars more sensitive due to the complexity and a lot more difficult and even more expensive to repair.

The ECU, however, helped ensure that our cars run properly most -if not all- of the time. The computer box now even sends errors and warnings before anything disastrous happens to your vehicle.

Computer boxes have gone a long way from when they first started out. Today they can control almost all the important functions within an engine, and beyond. Some might say that all-mechanical is still the way to go, but the computer box surely has made driving easier, more economical, and safer too.