Scan tools are a must in your diagnostic arsenal

May 7, 2010
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.

What is Mode 6?

Mode 6 is a diagnostic mode built into OBDII that performs on-board monitoring of test results for non-continuously monitored systems. Mode 6 data is real time and unrecorded, so it can reveal a lot of information about system faults like ignition misfire, fuel control and other engine management details. This means that Mode 6 data may be able to reveal a problem before it trips the MIL or sets a DTC. Albeit helpful, Mode 6 data may not be available on all scan tools or vehicle systems. Ask your equipment rep whether the scan tool you’re considering can tap into Mode 6 data. Within the last several model years, the carmakers have boosted Mode 6 availability, functionality and the importance of its data.

A diagnostic procedure I came across involves an actuator test. Is this something a scan tool can do?

Yes, depending on the system a scan tool’s connected to, it can perform different actuator tests. The scan tool essentially sends a command to an actuator, like a relay or solenoid, to see whether that actuator can really do its job. This capability also depends on whether the vehicle manufacturer enables this function in its onboard electronics.
Are scan tools mainly intended for diagnosing issues with engine controls?

Not anymore. Today’s vehicles are more interconnected and networked than ever. Multiple computers share information in an onboard network that controls all phases of vehicle operation. Scan tools can now “converse” with this network through bidirectional communications. This enables you to both read and send values to various onboard systems. This includes the Controller Area Network, entertainment and information systems, anti-lock brakes and transmission control.

I’d like to be able to access service information through a scan tool. Is this possible?

Yes, in some cases different scan tool manufacturers provide onboard service information through their tools. This can be a real time-saver when getting to the heart of system problems. Compare how this feature stacks up against your existing service information subscription.

What’s the best way to comparison shop for my scan tool needs?

Start by defining your budget and the population of vehicles you plan to service. Be honest about your needs. It’s not practical to invest in equipment for cars you never service, so stay objective about needed applications. Build a scan tool spreadsheet and enter your criteria into it as your research unfolds.

Next, talk to some tool and equipment reps about their offerings and add those details to your spreadsheet. Include a category for future expandability so you don’t overlook what could be possible to increase your scan tool capabilities.

Now, check around with other techs and shop owners about their experience with the scan tools you’re considering. If you’re a member of the PTEN-sponsored International Automotive Technicians Network (iATN) at, you may want to check into the Tool & Equipment forum there. There’s a lot of collective expertise on tap that may help guide your scan tool quest.

Can scan tools perform J2534 reprogramming functions?

In some cases, yes. Check with your equipment rep on the specific scan tool you’re considering to see if this is an option.

What about updates and subscriptions?

Scan tools handle application updates a couple of different ways. Handheld scan tools often use plug-in cartridge updates for new or different applications. PC-based scan tools usually update through a software download. The key thing is to be clear on how this works and the costs involved going forward. When it comes to scan tools, it’s not just the original acquisition price; you also have to keep update costs in mind going forward.

So, which scan tool is best for the money?

Because of the unique diagnostic needs found in every shop, what may be best suited for one shop may not be best for yours. When you get down to matching up with your exact needs, there may not be a single scan tool that matches up exactly. In the end, the best solution may be a couple of different scan tools, some based on different platforms. For instance, you may find that a hand-held dedicated scan tool works best for one segment of vehicle service, while a PC-based version works better for another. The key thing is to be patient and build the right match-up for you.

Upcoming Q&A sections this year will cover electrical systems tools, hand tools, and tire/wheel service equipment. Please send in any questions you have regarding those tool categories, or anything else.

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