What is CANBUS?

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, each component of the vehicle had to have its own wiring loom that used relays to control each part and fuses. CANBUS meant that the vehicle could be broken down into key parts, with the engine bay managed by an ECM or Engine Control Module, a door module controls central locking and window functions and a BCM or Body Control Module handles everything else. So instead of having loads of wires running through your car, you have a collection of wires for a function and then a couple of wires twisted together that send and receive the CANBUS signal through the vehicle.

What does CANBUS do?

There are 3 different networks in each vehicle, with the fastest in the engine bay and the middle speed network in the car and the slowest speed being the diagnostics port.

For instance, the ECM detects the lambda sensor is giving a reading that the engine is burning fuel too rich, it checks the temperature sensor to see if the engine is warm enough and regulates the amount of oxygen entering the engine to make the engine run leaner.

There are other effects you will only notice when you are looking for them, for instance when you turn the key, the radio starts and when you remove the key the radio stops. When you accelerate, the volume of the radio increases to mask the engine and road noise. As you break, the volume decreases. When you turn on lights, the illumination displays on the dashboard and the radio lights up. If you put the vehicle in reverse, the reversing sensors turn on and the radio may show indicators of how far you are from the object behind.

These all used to be managed with separate wires, but your radio manages this with just two wires because of CANBUS.

When can CANBUS be a problem?

If you buy an aftermarket car stereo that doesn’t understand CANBUS, you need to tap into a fuse that is turned off by the ignition switch or the stereo remains on indefinitely and could flatten the battery, also if you have aftermarket reversing cameras and sensors, these need to be powered from the reversing lamp bulb, so you need to splice into those wires.

There is another problem, whenever you open the driver’s door, which you do more often than the other doors, the mechanical action can cause the wires to break, and water can get into that location. When this happens, your vehicle will act like it is possessed.

My suddenly started trying to start the ignition, wipers going and all the dashboard lights came on, often after a rain storm but not during.

CANBUS decoder

A CANBUS decoder plugs into the cables between an aftermarket car stereo and provides the ability to control the behaviour of the vehicle as if your aftermarket car stereo could understand the CANBUS. Some aftermarket car stereos can work with the CANBUS network but need a decoder to reduce the voltage of the vehicle to a safe operating voltage.

This also means that the reversing camera and sensors can be powered from the decoder rather than tampering with the vehicle wiring. Your aftermarket stereo can then behave like the car manufacturer’s own stereo with much better features.

Share this post with your friends