There is something that is not working correctly in your Monitor System. If you have an emission component that is border line, like your CAT or an Oxygen Sensor, the Monitors will not set. Did you ever replace your CAT because if so, you may need a software update. And if it was not a factory CAT, the monitors will almost never work correctly.There is a large Technical Service Bulletin (23 pages) number EG003-02 about how set the Monitors for your vehicle, so Toyota knows about this issue. The best thing to do is to have a skilled Technician, first run this procedure and then check your Mode 6 data. This is pretty technical stuff, in that it is hexadecimal scientific data on the status of your your Emissions Monitors, Components and test IDs and results. I would NOT go to a dealer, because they often don' t do Smog. I do Gold Shield Smog Emissions work in N. California for a living. I would go to the best Gold Shield Shop in your area. Gold Shield Shops are required to know how to check Mode 6, which most shops and dealers are clueless about. I have to fix cars for the big Toyota dealer just across the Street from my shop every week, because they are lost. Dealers are often just parts replacement shops and not very good at serious Diagnostic any more.