Electronics and networks: how a car thinks

What the car's electronics do

A modern car is a network of small computers. Each control unit reads its sensors, decides what to do and drives its motors, valves and lamps: the engine, brakes, airbags, doors and climate each have their own. A new car has dozens of them, a well-equipped one more than a hundred, and they share information over data networks. The wheel speed measured for the ABS, for example, is also used by the speedometer, the gearbox and the cruise control. More and more of how a car behaves is decided by software, and many cars now receive updates over the air.

Where this page stops

This page is about how the electronics think and talk to each other. The power they run on, from the 12-volt battery to fuses and wiring, is in Electrical and in Lighting & fuses. What each dashboard warning light means is explained in Discover.

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Open Dashboard warning lights →

How car electronics are organised

Four stages, from one box per function to a central computer

Distributed: one unit per function

All types

The classic layout: every function got its own control unit, and each new feature meant another box. Engine, gearbox, ABS, airbags, doors and seats each have a unit near the parts it controls, joined by a few CAN buses. It is easy to develop piece by piece, but the wiring grows long and heavy, and the units come from different suppliers, each with its own software.

Components

A separate unit for each function
Several CAN buses
A gateway between the buses

Domain architecture

All types

Functions are grouped into domains such as powertrain, chassis, body, infotainment and driver assistance. Each domain gets a powerful domain controller that does the work of several small units. The domains talk to each other through a central gateway, more and more often over fast Ethernet. Most cars built today sit somewhere between this layout and the distributed one.

Components

Domain controllers
Central gateway
Ethernet backbone between domains

Zonal architecture

Mostly new electric cars

Here the car is divided by place, not by function. A zone controller in each area of the car connects and powers every nearby sensor, motor and lamp, whatever system it belongs to. The zones send their data over fast Ethernet to a central computer. The wiring becomes much shorter and lighter, and it is easier for robots to install on the assembly line.

Components

Zone controllers by location
Central computer
Much shorter wiring

Central computer (software-defined car)

Mostly new electric cars

The furthest step: one or a few very powerful computers run almost all of the car's software, while the zones only connect the hardware. New functions become mostly a matter of software, so the car can gain features and fixes through over-the-air updates long after it was sold. Carmakers call this the software-defined vehicle, and many new electric platforms are built this way.

Components

High-performance central computer
Zones that only connect the hardware
Over-the-air updates

Electronics by vehicle type

The same networks everywhere, with more to coordinate in electrified cars

ICE

The engine control unit is the busiest: it works out fuel injection and ignition for every engine cycle from dozens of sensors and works closely with the gearbox unit. Most petrol and diesel cars on the road use a distributed or domain layout connected by CAN buses, with a separate network for infotainment.

Hybrid

A hybrid needs a supervising controller that decides at every moment whether the engine, the electric motor or both drive the wheels, and how much to charge the battery. It coordinates the engine unit, the inverter and the battery management system, so the networks carry more traffic, and more of it matters for driving.

Electric

There is no engine unit, but the battery management system, inverter, on-board charger and thermal management have to work as one. New electric cars are often designed from scratch, so they were the first to use zonal layouts, a central computer and regular over-the-air updates that can change how the car drives or charges.

What the car's electronics are made of

Shown on a domain layout, the most common one today

Network overview

Click a node to see its description in the cards below

Control unit (ECU)

A small computer in a sealed box: a microcontroller, memory for its program and settings, a power supply and driver circuits strong enough to switch motors, valves and lamps. It runs the same loop all the time: read the sensors, calculate, command. It has to survive water, vibration and temperatures from about −40 °C to well over 100 °C.

Sensors

The car's senses. They turn temperature, pressure, speed, position, acceleration, the oxygen in the exhaust or the light outside into electrical signals a control unit can read. A modern car often has more than a hundred. Many are now smart: they send ready digital values over a bus instead of a raw voltage.

Actuators

The muscles: everything a control unit can move or switch. Electric motors for windows, seats and the throttle, valves in the brakes and gearbox, injectors, relays, pumps and fans. A well-equipped car has dozens of small electric motors, a luxury one can have more than a hundred.

CAN bus

The main network of almost every car since the 1990s, developed by Bosch in the 1980s. Two twisted wires carry short messages that every unit on the bus hears. Each message has a priority, so an urgent one from the brakes always gets through first. Classic CAN carries up to 1 Mbit/s and the newer CAN FD several times more: slow by computer standards, but extremely reliable.

LIN bus

A cheap, simple network on a single wire for jobs that do not need speed: window switches, mirrors, seat motors, rain and light sensors, wiper motors. One master unit asks and the others answer, at up to about 20 kbit/s. It saves wiring and money where CAN would be overkill.

Automotive Ethernet

The fast lane: the same idea as the network in an office, but on a single pair of thin twisted wires that cope with the car's electrical noise. Cameras, large screens, driver assistance and the links between domain or zone controllers need 100 Mbit/s to several Gbit/s, far beyond CAN. Its share grows with every new generation of cars.

Central gateway

The junction where the networks meet. It passes messages between the CAN, LIN and Ethernet networks, translates between them and decides what may go where: a message from the infotainment system should never be able to reach the brakes. It is also the entry point for diagnostics and software updates, so it plays a key part in protecting the car.

OBD-II port and fault codes

A 16-pin socket under the dashboard, required in the USA since 1996 and in the EU since 2001 for petrol cars and 2004 for diesels. A scanner plugged into it reads the fault codes that control units store when something goes wrong, often at the moment a warning light comes on. P0300, for example, means misfires. The first letter shows where: P powertrain, C chassis, B body, U network.

Software and OTA updates

A modern car runs on tens of millions of lines of code, far more than the space shuttle did. Over-the-air (OTA) updates deliver new versions through the car's mobile connection without a visit to the workshop: fixes, new features, sometimes even more range or power. The update downloads in the background, is checked, and installs while the car is parked.

Cybersecurity

A connected car can be attacked like any computer, so its defences come in layers: the gateway keeps the networks apart, a firewall filters the traffic, important messages are signed so a fake one is rejected, and updates must carry the maker's digital signature. Since July 2024 every new car registered in the EU must meet the UN rules R155 on cybersecurity and R156 on software updates.