Nissan Altima MIL Code P1126...
I posted a question within the past week regarding a 2001 Nissan Altima GXE on which a pending malfunction P1126 turned into a MIL Code and lit the "check engine lamp". From various web sites I found that the manufacturer specific code description of P1126 was "thermostat function". In a later conversation with a mechanic he told me that his information called it "thermostat stuck open". I was suspicious of this since the thermostat had been changed just 6 months ago.
As it turned out, for the benefit of anyone who offered me advice, and most of the tips were useful, the thermostat was fine but the garage who installed it did not have it centered up in the recess and a small constant flow of water was constantly bypassing the thermostat. This small bypass flow, although small, must have been sufficient to keep the initial thermal cycles detected by the "engine coolant temperature sensor" too small to be considered a functional thermostat.
I also found that a fiber gasket had been used and the instructions, although confusing seemed to imply that a "liquid gasket" or blue RTV sealant should be used in place of a gasket. The thermostat had apparently slipped down from the engine side recess and the fiber gasket held back the water for a while until recently when it severed through and permitted a bypass flow. I found the gasket cut in the area where it had been pinched by the careless installation. The job was done around December and it took until July and some long distance drives to show up.
Thanks to those who offered me advice on this problem. I initially eliminated the "coolant temperature sensor" by checking its resistance as the car cooled off after driving and found it to be about what the resistance chart claimed in the procedure from a hot engine to a cold engine.