What exactly is a CAN BUS in a Fiat Linea?

You may have heard this term being bandied about quite a bit these days when referring to cars, especially like the Fiat Linea, Fiat Punto, Volkswagen Vento, Honda City or even the Mahindra XUV500. Every time you think of a modification for your car, there are people who would warn you about messing with the CAN BUS.


What’s a CAN BUS?

A CAN BUS stands for “Controller Area Network” bus (system of information transport). IT geeks would be familiar with the term as it’s similar to your LAN (Local Area Network) system in your office or home.

So what exactly does a CAN BUS system do? There are two sides to a CAN BUS. On one hand, having a CAN BUS system in a car makes it much simpler to manufacture as it saves car makers acres of space and cost on complicated wiring.

With more and more electronics and conveniences being fitted in cars, the amount of wiring that has to go into the car gets incredibly complicated and not to mention messy, as there’s very little space to tuck in all that wiring. And, God forbid, if a rodent decides to chomp away at a couple of wires, all hell will break loose.

To give you an example, just look at the switches on the driver’s side door of any high-end car these days. It will have a row of switches for the power windows, at least four of them, plus a child lock function. It will also have an electronic locking facility on the door for the central locking system. It probably will also have controls for the powered outside rear-view mirrors, and may include an auto-folding system that operates with the central locking. It may also have memory and adjustment settings for powered seats.

If you were to imagine the kind of wiring all these controls would require, it’s huge. If there was no CAN BUS system, each power window wire will have to run from the driver’s door to the passenger door and back. Each mirror wire will have to run to the other mirror and back. Similarly with the central locking system and cabin lights. All this would result in a fat wad of wires snaking out of the door and through the cabin – totally impractical, expensive and a pain to keep tidy.

Instead, if you look at a car with a CAN BUS system, you’ll instead find just a slim cable going into the door from the fender area, not a thick wad of wires. What a CAN BUS system does is to “decentralize” the controls and electrical systems of the car and isolate them to local areas. Each local area has its own “microprocessor” or central control unit.

The Fiat Linea for instance has seven “microprocessors” or ECUs on board. It’s these microprocessors that act as local power centres and control all the functions in a given area. The driver’s door for instance will have one ECU in there which controls the windows, locks, mirrors etc. But when it has to send a signal to the other side door or window to open or close, it sends “packets of data” to the CAN BUS, which is a central data wiring system going all around the car to every component. This “packet of data” is picked up in a micro-second by the other door’s receiving unit that understands it and performs the function accordingly.

It’s because of such a CAN BUS network that finding faults and diagnosing problems becomes really easy. If a headlight bulb fuses for instance, the local microprocessor will not send signals of its functioning into the CAN BUS. The ECU then understands there’s a problem and sends an alert to the driver on the MID (multi-information display) saying “Right headlamp bulb not working”. Similarly when a door is left open, the ECU knows exactly which door is open and displays “Left rear door open” on the MID. It’s the CAN BUS that makes it possible for you to get multiple car settings at your fingertips – controlling the radio, voice controls, Bluetooth phone controls etc. All systems talk to each other.

The CAN BUS makes it easy to replace parts too. An entire module can be unplugged and plugged in again separately.

However, on the other hand, the CAN BUS can be a bugbear for those who want to modify their cars. Just how modification friendly is a Fiat Linea for instance? Fiat allows for accessories to be added to the car as long as they are CAN BUS friendly and engineered to Fiat’s standards. So if you were to add HID headlamps for instance on the Linea, you would need to source a set that are CAN BUS friendly (most good accessory makers make CAN BUS friendly accessories), so that the original software in the car can recognize the new light. Otherwise, just adding any aftermarket HID kit in a Linea will throw up an error in the software.

The advantages of a CAN BUS system are huge. Most carmakers are now slowly adopting this system, and very soon, it will be quite common on almost all cars.