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OBD II Emission Monitor Readiness

3 November 2011
Saskatchewan, Canada
I have weighed in on threads discussing problems with completing emission monitor tests and have PMd with at least a couple of owners who have had problems with getting their monitors set prior to the regular vehicle emission compliance test. It is not a particular problem for me because :

1) Saskatchewan does not have an emission compliance testing program and
2) for the first few years of ownership, every Spring after taking my car out of storage I would plug in the OBDII scanner after I got home just to see what was going on. In all cases after doing the start up / warm up / light check / leak check / listen for strange noises and then drive the approximately 30 km home I had always managed to set all the monitors (so far!).

My interest was more of an academic interest. I figured that if you knew what the monitor software was specifically looking to check it would make it easier to find deficiencies on your own car if you were failing to get your monitors set as opposed to just driving around in any of the various 'drive cycles' that you can find on the internet. I don't have to go through any heroic drive cycles on my Myr 2000 so others with stock cars should not have to do it either.

I have scrounged through a lot of the standards looking for guidance on how the monitors operate. I eventually came across this document

Performing Onboard Diagnostic System Checks as Part of a Vehicle Inspection and Maintenance Program (EPA-420-R-01-015, June 2001)

On page 10, last paragraph of the document, there is a little gem of info:

The algorithms for running these eight, periodic monitors are uniqueto each manufacturer and involve such things as ambient temperature as well as drivingconditions.

So the monitor routines are proprietary to the manufacture. Since that info is unlikely to be released by the manufacture that kind of dashes my hope of finding the algorithm. I expect that there must be some piece of regulation enabled by the legislation that sets out a functional requirement for the monitors (leaving implementation details to the vendor) ; but, I have not been able to find that if it even exists.

The EPA 420 document is interesting because it notes that some vehicles have some significant problems with completing their monitors. The document has a short list and OBD Clearinghouse has a more comprehensive list of those vehicles and the specific problems. For some of these vehicles they have granted exemptions on the requirement for setting the monitors because they have enough evidence that it is not happening. Honda and Acura vehicles are absent from that list with one exception. There is one Acura model that gets a mention because it has a problem establishing a link through the DLC with some scanners. The fix is to use a different scanner. No Honda / Acura vehicles are listed as having 'known' monitor issues.

The document does discuss the Evap monitor as being one of the most problematic monitors and for vehicles up to MYr 2000 you may be able to get a waiver if it is just the Evap which is not set. The Evap monitor does seem to be the most problematic one for NSX owners. In the EPA document there is some discussion of the roll of leaky gas caps in setting the monitor. By extension I would take it that if you have other leaks in the Evap system you would have a similar problem setting the Evap monitor and driving around in endless drive cycles isn't going to fix that problem.

So far, the only take away is that if you are going to try the drive cycle fix it is going to have to be a Honda drive cycle not a generic drive cycle because the monitor algorithms in the ECU are unique to each manufacturer. If you are having problems setting the monitors I think it is a sign of some other problem because the monitors on my car set without having to drive around at midnight under a full moon after having sprinkled the blood from a sacrificed chicken on the ECU.

I continue to scrounge around for information on how the monitors work, specifically what parameters they look for to establish a complete status. However, at present I am not confident that information is readily available.