What Do We Know About OBDII Now?

Illinois has been testing OBDII systems with pass fail criteria for about a year now, and we know much more about how the system works or does not work than we knew in January 2004. But first a quick review... A vehicle that is presented for an OBDII test will first receive a gas cap test and then be scanned through the DLC. The vast majority of the vehicles will in fact communicate via the DLC and most that will not are either missing B+ on pin 16 and/or ground on pin 5. If the vehicle will communicate via the DLC, a check of applicable readiness monitors will occur. If the correct number of monitors have been run, MIL function is analyzed and the vehicle passes or fails. This abbreviated explanation gives an overview of the test. More information is available in the Outreach OBDII seminars.

So what do we know about the test after months of testing thousands of vehicles? The first item of interest is the system is doing exactly what it was designed to do. Remember that OBDII is an emission testing strategy that includes most of the engine management functions that were present in OBDI. The design of OBDII is supposed to allow independent testing of emission functions with the ability to identify failures that might allow the vehicle to produce in excess of 150 percent of the Federal Test Procedure. Without a doubt it is doing exactly this. Technicians that attend the OBDII seminars indicate that vehicles that have the MIL illuminated or commanded on do have something wrong and can be fixed to a level that will allow the MIL to be commanded off by the PCM. There has been virtually no false MILs on vehicles. If the MIL is on - there are fixable problems. Once they are fixed the MIL will be commanded off. The system is doing exactly what it was supposed to do.

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