Q What is a CAN bus system?
Richard Redmayne, Dynojet UK This is a term you hear a lot when it comes to modern bike electrical systems. ‘CAN’ stands for Controller Area Network and ‘bus’ is a transmission path for transferring data on a system, which early computer designers thought was similar to a bus making multiple stops on a route.
CAN bus was developed by Bosch in the 1980s and first appeared in bikes when BMW fitted it to their K-series machinery with the first anti-lock brakes. Traditionally bikes have a multi-wire wiring loom to interconnect various electronic components on individual circuits.
A CAN bus system gets rid of that huge bundle of wires for one or two twisted wires connecting various Electronic Control Units (ECU) or ‘nodes’, saving space and materials for a cleaner way of transmitting data with no loss of integrity. On a bike those nodes could be ECUS for the anti-lock braking, dash, traction control, ride-by-wire throttle and electronic suspension; a Ducati Multistrada 1200 has six nodes.
The basic principle is that each node can send and receive messages, but not simultaneously. Those data messages have dominant and recessive bits, and depending on its programming, when a node is in ‘listen’ mode it can identify if the network message has priority and is relevant, so there’s no delay in the higher-priority message, and the lower-priority message is automatically retransmitted.
However, this ‘intelligence’ means that it can be tricky adding aftermarket components as the CAN bus will sense an additional power feed as an interruption in the data stream, and throw up an error code. But if you can find a way in, for example on BMW GSS you can take power from the COM port, then it doesn’t mind. It depends what it’s programmed with at the factory.
First seen on BMWS, CAN bus systems keep heavy wiring to a minimum