CAN bus basics


By MACS Technical Think tank

Automotive omputer technology has grown exponentially over the last several years. Processors are faster and smaller than ever before, automotive modules are more reliable and able to take the abuse of daily driving, and all of this is allowing vehicle manufacturers to provide consumers with what they want – more convenience and more comfort.
None of this would be practical without a means of allowing all the different modules to work together and share information. This is where the idea of the “bus” comes from. The bus is nothing more than a connection between modules that allows them to communicate with each other.

The network you may have in your shop that allows all the shop computers to access the same information and programs is the same concept built into today’s cars. Think of the bus system as a “phone line” that modules can use to “call” the other modules.
There are several bus systems in use on today’s cars, and may incorporate either a single wire or dual-wire network between modules. That car in your bay may even use more than one, depending on what systems are networked together. If so, keep an eye out for the “gateway” module. This module will have more than one bus system connected to it.
The gateway module is the “translator” that allows different bus systems to share needed information. Each system has its own unique methodology for communicating. Older bus systems typically assigned a master module that was in charge of the entire network, supplying the power to the bus and arbitrating the messages passed along the network.

In some designs, the failure of one module could cause the entire network to fail, and result in the dreaded “no communication” or “no bus” codes to be stored. The newest addition to the list is CAN, or Controller Area Network. CAN systems first appeared in some models in 2003, and the good news is that this is the protocol now required on every car manufactured starting with the 2008 model year.

When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.

If you’re a service professional and not a MACS member yet, you should be, click here for more information.

You can E-mail us at macsworldwide@macsw.org or visit http://bit.ly/cf7az8 to find a Mobile Air Conditioning Society member repair shop in your area. Visit http://bit.ly/9FxwTh to find out more about your car’s mobile A/C and engine cooling system.

The 32nd annual Mobile Air Conditioning Society (MACS) Worldwide Convention and Trade Show will take place January 18-20, 2012 at the Rio All Suite Hotel and Casino in Las Vegas, NV.

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About macsworldwide

Mobile Air Conditioning Society (MACS) Worldwide Founded in 1981, MACS is the leading non-profit trade association for the mobile air conditioning, heating and engine cooling system segment of the automotive aftermarket. Since 1991, MACS has assisted more than 600,000 technicians to comply with the 1990 U.S. EPA Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment. The Mobile Air Conditioning Society (MACS) Worldwide’s mission is clear and focused--as the recognized global authority on mobile air conditioning and heat transfer industry issues. www.macsw.org
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