Physically Connecting Machines: The Basics of the CAN Bus

by Brian Frederick
February 20, 2018

How Controller Area Network (CAN) buses connect your equipment

By now, you’ve probably got at least a high-level understanding of how telematics work and how they can help you streamline your fleet management processes. But what might still be unclear is how exactly telematics recording devices connect to your machine physically.

The short answer is that it connects through a Controller Area Network, or CAN bus. But unless you’re an engineer, that probably doesn’t mean much to you. With that in mind, we’ve created a layman’s guide to this vital link between your vehicles, equipment and your telematics platform.

What is a CAN bus?

A CAN bus is a way of connecting sensors and electronic control units like the powertrain module, speed control unit or battery management system. Clear as mud, right? Think of it this way: if your equipment was a human body, the CAN bus is the nervous system. It’s what allows all the parts to communicate with each other and report back to the brain. And like the nervous system, they are essential to many applications on your machines.

How does it work?

Most pieces of equipment have dozens of Electronic Control Units, or ECUs, overseeing nearly every aspect of a machine. These send data along a network known as the CAN. In some systems there is a primary controller keeping watch over the entire system, but one of the benefits of a CAN bus system is that this “brain” isn’t necessary — the system can operate without it.

To continue our nervous system analogy, the CAN bus is the entire system of nerves and synapses instantly carrying information throughout the network.

What are the advantages of a CAN bus?

The main bus is responsible for monitoring faults and diagnosing problems. This is a more efficient process than manually querying sub-controllers all over the equipment. It also reduces the points of failure. Because there’s only one data line, the risk of multiple connections failing is minimized. It also adds a level of redundancy in case one of the subsystems does break down.

Overall, the CAN bus is a lower cost way of machine communication and offers a level of flexibility that wasn’t available before they were developed.

How does the CAN bus communicate?

Each node in the network can both send and receive messages. They send a variety of information with every message it sends out over the network. The major components are:

• Start-of-frame (1 bit) — This tells nodes that a message is incoming

• Identifier (11 bits) — This says where the message is coming from. Lower values have a higher priority (temperature, RPMs)

• Remote Transmission Request (1 bit) — Allows nodes to request information from other nodes

• Data Length Code (4 bits) — Tells nodes how much data is being transmitted

• Data (0-8 bytes) (0-64 bits) — The actual data transmitted

• Cycle Redundancy Check (15 bits) — Used to ensure the data isn’t corrupted

• Acknowledgment (1 bit) — Indicates that Cycle Redundancy Check was successful

• End of Frame (7 bits) — Marks the end of the message

As you can see, there’s a lot of data included in each CAN bus message. And if taken in its raw format, it doesn’t make much sense at all. That’s where a platform like ES Track comes in. ES Track takes the raw data, which just looks like a bunch of random numbers and letters to most people, and uses it to generate reports on your equipment.

The end result is you get lots of in-depth information on each asset in your fleet; things like runtime, engine temperature and oil status. You can quickly and easily run diagnostics on any machine from anywhere, identifying potential problems and improving overall machine health. This, in turn, leads to better overall fleet efficiency and more profitability. And it all starts with the small but complex system known as the CAN bus.

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