People need to get it out of their head that a oxygen sensors cause check engine lights so much. I work at an auto parts store and do scans all the time. They are indeed very common, just not as common as 90% of the people who come in think. I've watched so many people throw so much money away on replacing oxygen…

A stuck thermostat is an emission related issue. Wrong combustion temperatures, ECM stuck in open loop mode, and probably not heating the catalytic converter enough for light off. Cold temperature is probably the worst of the emissions issues.