Tales From the Bench - October/November - 2017

Scan Tool 101

In the transmission industry, there’s something new to learn every day. Some of the simplest things can be challenging, but that’s what we enjoy: fixing problems and overcoming challenges.

Gathering information and saving it is just as important as working on the cars themselves. In this article, we’ll discuss an easy way of gathering and saving data that you can use to find the information you need.

Code Readers — A code reader can be a fast-and-easy first check for pulling diagnostic trouble codes. Many technicians have discovered they can retrieve OBD-II codes with a code reader that a large scan tool might miss. But never clear the codes after using a code reader to check for codes. Code readers are almost worthless for PIDs. You need a full scan tool for everyday diagnostics.

Aftermarket Scan Tools — There are many makes and models of scan tool on the market. And no one scan tool is better for every purpose or every shop.

When looking for a scan tool, first ask yourself:

  • What type of vehicles will you use it for most? Many shops have two or three go-to scan tools for this reason.
  • Do you want a separate scope or have it as part of the scan tool? A scope is a must-have for today’s technician.
  • Does the scan tool offer movie or data recording? This is another must-have for today’s cars and trucks.

OE Scan Tools — An OE scan tool is a terrific tool for diagnosing one particular car line, but it’s hard to have one for every manufacturer.

In the future, many shops will need to have a few factory scan tools for normal day-to-day work. The reason? Data and testing is better and faster. Programming is safer with the OE scan tool and faster in many cases. If you do a lot of Dodge programming, a factory tool is the way to go.

When doing general diagnostics, you’ll probably want one tool that’ll be useful for most vehicles, such as a Snap-on scan tool with a scope and meter built in. Just grab the scan tool with two leads for doing basic checks. Before starting the car, you can set up the meter function to read voltage.


If you answer these 4 simple questions on every car you work on, you’ll have fewer difficulties with your repairs:

  1. What’s the battery voltage before you start the engine? (figure 1)

    This is the battery voltage “at rest”; after the car has been sitting without the engine running for an hour or more. If you don’t let the car sit, the reading won’t be as accurate.A fully charged battery should have 12.6 DC volts at 80ºF (27ºC). If it’s 12.4 volts, the battery is only at 75% and needs to be charged.

  2. What’s the lowest voltage during engine cranking? (figure 2)

    This is the voltage at the battery terminals when cranking the engine.A scope or graphing meter is great tool for this test. You can also use your meter’s Min/Max setting to capture the lowest voltage level while cranking.

    Generally look for 10 volts or more at summer temperatures. When they drop below 10 volts, you should probably start checking cables and connections. The numbers may be lower at colder temperatures.

    The best way to develop your own version of “normal” is to perform this test on every car or truck and see what voltages are when you have a cranking problem.

  3. What’s the voltage with engine running? (figure 3)

    With the engine running and electrical loads on (headlights, blower motor, etc.), look for at least 14 volts at around 1800 RPM. On newer cars, this voltage may drop to reduce engine load when the system is fully charged.

  4. What’s the voltage drop on the ground and power circuits? (figure 4 & 4a)

    For this, you’ll need to perform a voltage drop test on the ground and power circuits. Make sure you perform these test with the circuits live and under load.


After checking the battery and the electrical system, you’re ready to check the computer system:

  • Check and record all codes from all computer systems in the vehicle.
  • Check for freeze frame data.
  • Check all codes again.
  • Go to the troubleshooter to gather any data necessary on the codes.
  • Check data and reproduce complaint.

There are some really cool features on this scan tool:

Guided component test for each car — Enter the VIN and you’ll get a guided tour of what scope leads go where, what good patterns look like, and many useful tests.

Previous vehicles and data — where you’ll find stored movies or data files. This also helps when you’re reconnecting the scan tool after repairs; it saves all the VIN information from the earlier test.

Tools — where all the settings are. This is where you’ll find operating system and other functions.

OBD-II Health Check — the best place to start when pulling codes and gathering information. Don’t clear codes yet; you want to check all the systems again.

  • Go to codes menu.
  • Gather and record code information.
  • Go to troubleshooter or, better yet, Prodemand/Alldata to get code descriptions and learn why the code sets. The code description is often incorrect in different scan tools.
  • Go to the data and see what’s going on: TCC slip, voltage, temperatures, range switch, and more. Remember, the data from the scan tool is what the computer sees.

For example: The transmission doesn’t shift but the scan tool shows the solenoid turning on and off. Connect a meter to the solenoid command wire to prove the computer is sending the signal. It isn’t uncommon for the scan tool to indicate the command but there’s no signal from the computer.

You can perform functional tests on different circuits and for EPC testing.

When you’re checking a problem, always check all modules, even if you don’t think the problem could be related to that module. Engine codes can often cause transmission issues, as can codes for the transfer case, antilock brakes, body control module, and even airbag systems.

If you get U-codes, make sure which modules are providing data and which aren’t.

You have two ways of looking at data: You can look at the PID list and get a good idea of what’s going on with the system. Then you can go to graph mode and zero in on any specific problems.

Graph mode makes it easy to see what’s going on because it “draws a picture” for you. And you can use it to check each PID.

A few things to remember: When the scan tool is plugged in and viewing data, it’s recording the information. It has a buffer; this scan tool stores 2000 frames. When the buffer is full, it’ll overwrite old information with new. This can be very helpful on test drives and intermittent issues. When problems occur, just save the information. Never try to look at the scan tool while driving!


Here are some helpful web sites you should know about:

www1.snapon.com/diagnostics/us/SSC/DownloadPage.htm — Snap-on download site for ShopStream, used for viewing Snap-on movies, and it’s free!

www1.snapon.com/diagnostics/US/CC.htm — Snap-on training, and support for all their scan tools. This is an awesome place to get information for using your scan tool and tips for diagnosing issues. You can download a lot of manuals here, and find great information on how to save movies and connect to your computer.

www.valvebodypros.com/scanner.html — Valve Body Pro offers information on how to record movies for a few different scan tools, and useful information in their resources section on transducers.

www.revbase.com/BBBMOTOR — link to free TSB and wiring. Don’t forget about this site. The stuff here often isn’t available through Prodemand or Alldata.

www.nastf.org/i4a/pages/index.cfm?pageID=3292 — a list of all OE web sites that offer OE information and programming data. The links are free but the web sites aren’t. Most OE sites allow you to look up programming information for free to see if you need an update.

The scan tool is a wonderful device and can be invaluable for diagnosing computer systems. But they aren’t all the same, so make sure you have the right ones available; you’ll find it’ll cut your diagnostic time and improve your bottom line.