Your Scan Tool's Most Important Functions

Dave Cappert examines the most important scan tool functions.


Most scan tools can perform bidirectional communication where the tool can be used to “talk” back and forth with various onboard systems. Some examples include body computers, the Controller Area Network (CAN), entertainment and information systems, fuel control systems, anti-lock brakes (ABS) and transmission control.

Signal Substitution

Some scan tools can substitute values to check the response from the PCM. For example, a vehicle speed sensor (VSS) can affect several systems, like cruise control, speedometer and transmission. By substituting a value, you can quickly emulate different speed conditions that may prove useful during diagnosis.

Onboard Service Information

Current scan tool offerings often include onboard service information, which can be a real time-saver when checking whether a problem may be related to a service bulletin or to access further details from a schematic. Although it’s not a substitute for a service information system, this feature can be a time-saver.

The “Best” Scan Tool?

Questions abound when it comes to choosing a scan tool. Aftermarket-type or OE version? Traditional type or PC-based? The answer depends on your specific needs.

Carefully consider the makes, models and types of vehicles you service regularly, along with those you plan on servicing down the road. Talk over your options with other techs and your equipment rep. Above all, get some hands-on time with whatever scan tool you’re considering. In some cases, multiple scan tools may be necessary to handle the specific population of vehicles that come into your shop.

Also, like it or not, a scan tool is not the single answer for all your diagnostic woes. Onboard diagnostics really help, but they're no substitute for a thorough understanding of how the system works, how to conduct other pinpoint tests, and what other testing equipment might be needed.

Questions about this article? Contact the author, Dave Cappert at dcappert@gmail.com

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