What is CANBUS?

Onboard Diagnostics (ODB-II) port on a vehicle used to connect a cable to a reader to read the car's diagnostic information

If you are a driver, you probably have no idea what is going on in your vehicle. CANBUS is the benefit for all vehicle manufacturers and it is is partly to do with the diagnostics port on your vehicle known as the OBD port or On Board Diagnostics but plays a much larger picture in your vehicle.


Before 1995, vehicles were much simpler to maintain by garages and much simpler for vehicle manufacturers to create vehicles.

However, there was a growth in emissions testing and need for diagnostics in vehicles so the rudimentary OBD port was created.


CANBUS or Controller Area Network is a network inside your vehicle and has become a godsend for the manufacturer.

Before CANBUS, cars had huge wiring looms that ran around the car in various places because everything needed its own fuse and relay to work, so all that extra wiring was needed to provide power. CANBUS simplified everything, so in key locations there is a module that controls the functions of that area. The Engine has its ECU (Engine Control Unit) or ECM (Engine Control Module) and then there is one for the powertrain (if you have an automatic); the driver’s door has the door control module that handles the windows and the locks; there is also the BCM or Body Control Module that tends to live under the driver’s steering wheel or in the footwell of the passenger side that controls the radio, the horn and the lights.

Everything is connected together with just two twisted signal wires, and one 12v supply wire. Ground provides the return.

How many CANBUS networks are there?

There are 3 CANBUS networks in a car, a high speed network for the engine bay because the car needs to know in real time what temperature the engine is, how many revolutions the engine is turning and it’s precise position together with how lean or rich the fuel mix is.

The medium speed network does everything inside the car itself and relays information between the engine bay and the driver. As the driver accelerates, the radio volume increases to muffle the engine sound, the wipers move quicker to clear the screen and if the driver turns on the lights, the radio display dims and turns on lights on the buttons.

There is another CANBUS, this is for onboard diagnostics and is a slow speed network to be read via the OBD port.

When can CANBUS be a problem?

I had a problem with my car in that the driver’s window stopped responding one day, so I thought it was the motor. A few months later, after some heavy rains the car started to behave like it was possessed. The wipers would start moving erratically, the headlights and indicators would flash and then the engine tried to start by itself. Then the alarm would go off.

The problem was that the 2 signal wires had worn because the design of driver doors are to be opened more than the other doors, and the wires had broken and got wet.

Another problem with the CANBUS was when I installed an aftermarket radio. The stock radio has a built in decoder that detects when the engine is turned on, so the radio would play and turn off when the key was removed. Aftermarket radios don’t have decoders in them to detect the key action, so I had to use a wire from the rear wiper fuse to power the radio. Its an old school solution for a modern problem.

A CANBus decoder module converts the signals sent around the car into functions the radio can use such as power on and off, dim and brighten the display when the headlights are turned on and increase or lower the volume based on vehicle speed and open windows.

CANBUS decoder

A CANBUS decoder is a device you can connect to an aftermarket radio that interprets the vehicle’s codes that tell the radio to turn up the volume when driving faster and to dim the screen and activate the lights on the buttons. Additionally, it carries other information, such as for steering wheel controls and for when the vehicle is put into reverse so it can enable a reversing camera or detector.

Share this post with your friends