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What Do Emissions Control, Diagnostics and Troubleshooting, OBD-II and CAN Protocol Have to Do with Each Other?
Rena Ayeras

As mentioned in a previous article, What’s New About CAN FD?, the creation of the Control Area Network (CAN) bus started in 1983 at the Robert Bosch Company.

After finalizing the first design, the CAN protocol was introduced to the Society of Automotive Engineers (SAE) in 1986. In 1991, the CAN protocol was publicly released by its usage in the Mercedes Benz W140.  Since then, the conversion of mechanical devices to electrical components fabricated with integrated circuits has continued to grow. In addition to providing more features and lighter, smaller cars, the CAN bus has been integral for managing diagnostics and in 1996, became an essential part of environmental emissions control.

How and Why OBD-II Started

The On-Board Diagnostics (OBD-II) has been heavily used for monitoring emissions control and to minimize the pollution generated from fuel-driven vehicles. In 1996, OBD-II became mandatory for all cars and light trucks sold in the United States. In 2005, heavy duty vehicles were included.  In 2001, the European On-Board Diagnostics (EOBD) standard became mandatory for all gasoline powered vehicles sold in the European Union. Diesel powered vehicles were added in 2004.

How OBD-II Helps the Automotive Industry

Check Engine Light

You’ve probably seen that Check Engine light turn on and stay on, and after it’s been on long enough, you take it to the mechanic for diagnostics. The mechanic connects the OBD-II scanner to the OBD-II port of your vehicle to read and interpret the Diagnostic Trouble Codes (DTC). Many of these codes are related to performances that affect emissions.

Manufacturers also create codes to monitor their vehicles, a method of collecting data to determine what can be improved, as well as find defects and take remedial action. How about other information?

OBD-II Specification Includes CAN Protocol

The CAN protocol is one of the transport protocols of the OBD-II specification and is normally part of the OBD-II Data Link Connector (DLC) connector.  A universal DLC connector is illustrated below:


Pin 2 - J1850 Bus+
Pin 4 - Chassis Ground
Pin 5 - Signal Ground
Pin 6 - CAN High (J-2284)
Pin 7 - ISO 9141-2 K Line
Pin 10 - J1850 Bus
Pin 14 - CAN Low (J-2284)
Pin 15 - ISO 9141-2 L Line
Pin 16 - Battery Power

In addition to gathering DTC information, the OBD-II connector can be used to access raw CAN bus data, which can be helpful when important information is not available via OBD-II or manufacturer standards.

Diagnostic Tools for Analyzing Raw CAN Data

In addition to the OBD-II connector under the dashboard, there may be additional connectors under the hood of the vehicle, such as access points that are specific for the CAN bus. Vehicle diagnostics with voltage meter and laptopTo look into the details of CAN data packets, Total Phase offers a variety of CAN tools, including free software options, API commands and easy to use GUI , to fine-tune the troubleshooting and diagnostics. Like the meter shown above, a Total Phase Komodo CAN Duo (or Solo) Interface can be connected between the CAN bus and your laptop, allowing you to non-intrusively monitor and filter the data in real time, as well as save for further analysis. Here is a video that demonstrates using a Komodo interface with Data Center Software.

If you’d like more information about Total Phase developments for CAN tools, please contact us at sales@totalphase.com.