I have a 2001 Pontiac Aztek issue. My service soon light came on (its the car picture with wrench). Thought it was related to the oil as it was due to be changed. The mechanic hooked it up to a computer and the code came back as the temperature sensor. A few weeks prior I noticed that the temperature guage was reading correctly (stuck on cold), even when I drove it around town all day. Two days later I was travelling out of town (got an hour away) and without warning it stalled. It had almost a full tank of gas (3/4), conditions were cold with snowy road conditions. It wouldn't start, but would turn over. A gentleman stopped to help and said that it seems to not be getting any gas. He added a gas line antifreeze to fuel and it started within 5 minutes. I let it run for about another 5 minutes before proceeding on my way and 5 minutes later my engine light came on. I didn't want to take any chances so I turned around and headed back home. I'm not sure what's going on but could this be related to the temperature sensor being bad? Or even a thermostat issue or could this be fuel related like the pump (fuel filter replaced July 2010 with 6 injectors). Could anyone help with this issue? I know that the fan runs after the engine has been turned off for awhile too.

If your temp gauge is reading at cold even after driving for sometimes, then your thermostat is stuck shut; which means your water flow is minimal. I am surprised you have not overheated from this. I highly recommend replacing the thermostat, and check all water hoses, as well as replacing the temperature sensor. By replacing both - you'll have proper water flow to the block, and your temp gauge will be accurate. As far as the fuel, each time you fuel the vehicle, do as the nice person did, and add a fuel additive that he added - feul tanks and cylinders collect condensation and thus water down the fuel; the fuel treatment dries up the condensation (and prevents further). You only need to do this when it's really cold out - however, it is helpful to do so even in warmer temperatures to help keep fuel lines, and injectors clean. Consider also replacing the fuel filter; filters wear down and microscopic particles get logged into the injectors, which plugges them, causing any one or more cylinders to fail from firing correctly due to loss of or lack of fuel.
Last but not least, since the water/anti-freeze needs to be drained to replace the thermostat, have the engine flushed, and put new antifreeze (I suggest not using 50/50) as it's predeluted; though it works, the 100% antifreeze is best for colder temperatures. Speak with the auto parts dealer or your mechanic about this option, as well as their advice.

Please let me know if you need further assistance.
carsandcomps,
Guru, Premium Expert @ Fixya.com

Your temp sensor reads your coolant temp just like a thermometer. It also tells your computer when to turn your fans off and on. GM's have a problem not only with the sensors themselves, but also the wiring to them, so I would have it changed and the "pigtail" or wiring plug in at the same time. The stall sounds like water in the gas which has become a real problem whenever gas prices go up. Start with the sensor, it shouldn't be expensive, and if it fixes the problem, it will save you on your mpg and more expensive repairs down the road.