Information Overload

Is there information overload with OBD II?

Information is a good thing. It can be more effective than any tool in the light-duty technician's toolbox. But when a technician has too much information, it can become a bad thing, leading to confusion, hasty decisions and wasted time.

OBD (on-board diagnostics) II is a case in point, according to Mike Fahrion, director of engineering for Ottowa, IL-based B&B Electronics, maker of AutoTap diagnostic tools. Fahrion sees more and more OBD II vehicles finding their way into fleets these days, and technicians are not always trained to make sense of the onslaught of diagnostic information that is available.

"With all the outstanding diesel pickup trucks out there today on heavy duty chassis that have migrated to OBD II, with the PowerStroke and Duramax engines, and the Sprinter Vans that are under the OBD II flag, they're finding their way into all kinds of delivery fleets," he says. "Suddenly the maintenance folks are dealing with a lot more light-duty, OBD II stuff than they used to."

Jorge Menchu, president of Fresno, CA-based Automotive Electronics Services, Inc., agrees: "The bottom line," he says, "is that there's a tremendous amount of information, and it's absolutely overwhelming."


At first glance, it doesn't make sense that a system that has been used with great success to make diagnostics simpler could actually be creating more complexity. But a lot depends on the diagnostic tool being used, the amount of technical documentation available, and the experience of the technician.

"In theory, (OBD II) gives you a code and a short description, and if you have the right technical data you can go back and that'll launch you into a troubleshooting tree in your documentation," says Fahrion. "Maybe a lot of these guys don't have that to start with if they've got a real mixed fleet and they've got five of these and two of those and twelve of these. They're probably not going to be going off and getting training from GM or (any other OEM), so I don't know if they have access to all the data. They might be flying blind.

"Usually the first reaction you see, whether it's a do-it-yourselfer or a pro, is parts swapping," he says. "They don't know what the heck to do, but they know they have to do something. So much time and money gets spent that way."


One reason OBD II seems to get more complicated is that it is infinitely expandable. But so far, at least, every code follows a basic pattern.

"Usually you start out with a 'P,' so that tells you it's a powertrain code," Fahrion explains. "It could be powertrain, it could be body or chassis, or in an unusual case it could be 'U' for network. Then you've got your four digits after that. In theory, when you put all that together, you've got three one-line code descriptions that should give you some pretty good pointers towards what's going on.

"The first digit is the important one: if it's a zero, it means it's a generic code, and if it's not a zero that means it's a manufacturer's enhanced, or proprietary, code," he says. A generic 'P-zero' code, for example, points to an emissions-related problem, indicating that the engine is running in a way that could potentially affect emissions.

"That (generic code) can be a sign of trouble, but not necessarily," Fahrion explains. "Usually, the proprietary codes are there to supplement the generic codes. So, for example, if you have a misfire going on in a General Motors vehicle, you'll get a P code, maybe a P0300, which means you have a general misfire problem. But, when you go read the scans with the appropriate scan tool, it might also give you a second code that might pin it down to the exact cylinder. It might read 1304, for example, and that would mean that it's cylinder four that's misfiring. So the enhanced code is designed to give you more granularity than what the EPA decided the generic codes would be."

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