Scan tools are a must in your diagnostic arsenal

Technical Editor Dave Cappert answers your questions about scan tools.


Scan tools, although common, are also commonly misunderstood. These widely popular tools have certainly come a long way since 1980 when GM provided an Assembly Line Diagnostic Link (ALDL) as a means of checking out onboard computer functions at the end of the assembly line. Almost overnight, the service industry adopted this connector as a window into the onboard computer’s “mind” during vehicle service. When connected, a scan tool enabled a technician to look into this window for the first time, changing the course of vehicle diagnostics forever. The diagnostic platform has evolved progressively since those early days.

I’ve heard that all scan tools are pretty much the same since the EPA made up the requirements for generic OBDII data. Is this true?

No. Although the EPA established regulations for generic OBDII data, the generic data may not yield specific or sufficient details you may need when diagnosing certain systems. For the best diagnostic match-up, always consider the types of vehicles and systems you plan to work on, in relation to the breadth and depth of diagnostic information available from a given scan tool.

Since I already have a digital multimeter and an oscilloscope, do I really need a scan tool?

Retrieving Diagnostic Trouble Codes is the most common need for a scan tool, so it’s a definite yes. The codes usually trigger the Malfunction Indicator Lamp inside the vehicle. Code chasing has taken on additional relevance and significance with states adopting OBDII checks in place of tailpipe testing for state emissions programs. As important as codes are, they simply indicate the area/system of a fault, but not the fault itself. Here’s where additional scan tool functions, and your other equipment, come into play. Again, be sure the scan tool you’re considering is capable of providing sufficient details for the vehicles you service.

Can a scan tool help me with reading and interpreting serial data?

You bet. System problems do not always register as trouble codes, so the diagnostic process is not always related to the pursuit of a code. This is where a scan tool’s ability to display serial data, or Parameter Identification Data, may come in handy. For example, a vehicle may exhibit a drivability problem that does not set a code, yet undeniably possesses a performance problem. By taking a look into the heart and soul of the Powertrain Control Module, you can learn a lot about whether sensors and their operating ranges fall within specified values. Like codes, serial data helps to tell part of the story, but not all of it.

Is it better to go with a PC-based scan tool, or a dedicated hand-held version?

It all depends, as there can be advantages to each. For instance, a PC-based scan tool may be the ticket if you have a laptop available that can be piggybacked for vehicle diagnostics. The expandability of the PC platform, along with dropping hardware costs makes this platform a compelling choice. PCs also have larger displays than most handheld scan tools so that’s a plus. Some manufacturers also make scan tool software for handheld PDAs such as Pocket PC or Palm. Hand-held, dedicated scan tools, used to provide scan-tool only functions, but that’s all changed. Newer models have built-in oscilloscopes and multimeters, bridging the gap between pinpoint test equipment and the scan tool. Finally, while one platform may seem to be a better choice for you than another, first make sure that it can handle the vehicles you need to service. Applications come first, platform second.

Are OE scan tools generally better than aftermarket scan tools?

First, “better” is a relative term. What may be better for one situation may not be better for the next. Generally speaking, an OE scan tool will provide excellent depth into the vehicle applications it covers, but little to no breadth over other makes of vehicles. Conversely, aftermarket scan tools can generally cover a wider range of vehicles, but may not have as much depth for diagnostics in given applications. Again, it depends on your specific needs.

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