Recently, for the second year in a row, I had trouble passing the emissions test. The reason was that the "monitors were not ready". I thought my computer was kaput last year so I purchased another one from autoecms.com. I had to drive my pickup around for a week or so before it would "Pass". This year my truck failed again, for the same reason..."monitors not ready." So I drove around for a week, and it failed again. At this point I was advised to make an appointment with a certain person at the local Dept of Public Health and have my vehicle evaluated there, which I did. At that evaluation (during which my vehicle was plugged into what I think was OBD II diagnostic equipment), I told my story about replacing the computer last year. It was explained that the "monitors" were really only the computer MEMORY. If the power is cut to the computer, the MEMORY is deleted. I've had no work done recently on the vehicle, nor has the battery been disconnected for any reason. It was his opinion that my 96 Nissan King Cab Pickup might have a "short" somewhere in the system that prevents the computer from getting a constant 12 volts of power. He reckoned that even if all the "monitors" had reset, if I went over a bump on the way to the testing station and shorted out the MEMORY in the computer, it would fail the test. By the way, there are no red warning lights on on the dash. Eventually the Health Department gave me a special pass to get my vehicle tested by the tailpipe. I passed and am set for another year. However, he told me to "get it taken care of" by next year. If a short circuit is the problem here, it would be VERY difficult to locate.
I'd appreciate hearing from anyone who has any experience in this matter.