Not long ago, the scan tool was simply one of the tools you could use to help diagnose emissions problems. My, how times change. With more states and programs adopting OBDII malfunctions as the pass/fail cutoff, the scan tool has now moved up the ranks as one of the key tools for diagnosing emissions problems.
Of course, all things being equal, this doesn't mean your gas analyzer and other diagnostic equipment is now obsolete. Let's just say that the voice of your scan tool is now on more of an official level.
Codes and beyond
Although trouble codes are the key element for analysis with respect to OBDII and emissions programs, a scan tool can do a lot more. For instance, a scan tool can display serial data, parameter identification data (PID), perform actuator tests and even interact with other onboard systems such as antilock brakes, transmissions, cruise control and body control.
Which one is best? Do you choose aftermarket or OE? Should you go with a handheld version or PC-based? It all depends.
It's not uncommon for technicians experienced with OBDII diagnostics to have a certain preference of one scan tool over another, depending on the make, model and year of cars they service. You need to consider this carefully before making a choice.
It's also a plus to chat with fellow technicians beforehand. Before you buy anything, spend some time behind the controls with a no-obligation trial. Remember, the choice you make needs to be your friend on a daily basis, so be patient with your search.
When the standards for OBDII-compliant scan tools were first being developed, EPA set out to standardize diagnostic trouble codes, along with some other things. The idea was to give scan tools "universal" capabilities that would work on all systems regardless of make. In the end, the standardized trouble codes are really not standard at all.
Let's examine the symbolism behind OBDII codes. OBDII codes contain
five characters, with the first character being a letter, and the remaining four characters
as numbers. The letter is important because it represents the specific system where the fault
• P indicates a powertrain-based code.
• B indicates a body control system code.
• C indicates a chassis control system code.
• U indicates a UART communications data link, network code.
The first character to the
right of the letter, which would numerically represent the thousands position, will contain
either a zero or a one. A zero means that the code is generic and therefore common to (almost)
all manufacturers (as standardized by SAE). The No. 1 in the same position means that the
code is manufacturer-specific. Moving to the right, the number in the hundreds position expresses
the specific vehicle system as established by SAE.
• No. 1 indicates an air metering/fuel system fault.
• No. 2 indicates a fuel injector fault.
• No. 3 indicates an ignition or misfire fault.
• No. 4 indicates an emission control fault.
• No. 5 indicates an idle speed control or vehicle speed sensor fault.
• No. 6 indicates a fault in the PCM output circuit.
• No. 7 indicates a transmission/transaxle fault.
The remaining characters in the tens and ones positions indicate a specific part of the system that may be at fault.
For the sake of our discussion and to demonstrate the difference in codes, it's important to note that the guidelines for standardizing codes only apply to P0xxx-type codes. In other words, on a powertrain-related code with generic application. However, a P0440 code on one make of vehicle may have a slightly different definition than on another make and model. Such an example is hardly a "universal" code.
Information is key
Because of the disparity of codes between makes, manufacturers and even model years, it's important that you have access to a reliable and current service information system. This is important for a couple of reasons.
Technical Editor Dave Cappert answers your questions about scan tools.
Dave Cappert examines the most important scan tool functions.