Problem with my thermostat? CAR?

[Javier]

I have a Mustang 2002 and Today i was driving it in the city for about 15min and I went to a store for about 5 min and after I turned my car back on and I my SERVICE ENGINE LIGHT turned on I and started driving again and my thermostat was all the way to cold, and wasnt even reaching the C. It was as if I had my car turned off. So i pulled over and I turned off my car and then back on and the thermostat was back to normal "in the middle" and right before i was about to stop at my house, I was driving at about 10mph, the thermostat all of a sudden went from being in the middle of C and H to the left of the C, like if my car was turned off.

ANY ONE HAVE AN IDEA OF WHAT IT COULD BE and how to fix it? Thank you.
WHEN I TRIED TAKING MY KEY OF THE IGNITION IT WAS KIND OF STUCK OR IDK WHAT HAPPENED THERE.

[Tony]

If the service engine light is still on then go to either, Advanced auto parts, auto zone or O'Reilly and have them scan it to find out why it's on. It sounds like some sort of electrical problem. If you have a Facebook then join this mustang group. alot of people ask similar questions and almost always get them answered. https://www.facebook.com/groups/NewEdgeMustangs/

[658]

Stop the car, and get out and open the hood and put your hand on the engine. If you get a burned hand, then you know the engine is hot. Temperature sensor (is what makes the gauge work), It either has a bad sender wire to the gauge or the sensor itself is faulty. Cheapest fix is to first rewire the sender with a new hot wire to the gauge. Chance are that goes through the ignition switch so it is there that the problem is most likely.
. If you have a "ton of keys on the key chain" then that weight could wear out the ignition prematurely.

[Michael]

Low on coolant? Air in cooling system? Sensor can not sense the temp as we'll through air.