trouble codes

I own two prius cars, one is a 01 with 126,000 miles and the other is a 02 with 27,000 miles on it. My 01 is the one I have questions on it is giving me the signal when I first start it that I need to take it to the dealer immediately for service. The check engine light also comes on when this happens and the code is always 3191 which is something to do with air fuel and emissions. I can clear the bar off the dash by a trick I learned several years ago by inserting the key twice with the drivers door open then shuting the door twice and inserting the key once and shutting the door three times and turning the key to on and off and removing the key. The car will drive fine and the check engine light will stay on until I clear it with a code reader. I had the same problem with the car when I first got it and had to replace the accelerator module to fix it which I had done when the dealer checked the batteries on a recall notice. I was wondering if anyone has seen this problem, it seems to occur the first time I start the car in the morning.
Tom