here is some good info on how to reset it:
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"This morning when I left it was 44*. I remember thinking, how odd...that is what temp it was when I pulled into my house last night. Well by 11 oclock I was sweating and it was still saying 44*. The compass was working so I figured it was one of two things. Either my temp sensor was bad or it was disconnected somehow. So I tried to manually reset it first before opening the hood.
Here is what you do, it is very simple if your temp display is stuck or not working properly. This ONLY applies to North American vehicles.
First off, go to an empty parking lot and put the truck in park and leave it running. Why will be explained in a moment. Hold the mode button down for about 10 seconds. At this time a number will appear between 1 and 15. Whatever number shows is the time zone that your truck is in. What it is going to do is calibrate itself to the earth (by reading the magnet polar reading from the earth). So go through the numbers until you get BACK to the number you are on. Example, I am in time zone 8 according to the service manual.
Once you get back to your time zone, quit pushing the button. Within a couple of seconds the line underneath your direction should be flashing. This is letting you know it needs to calibrate. Now put the truck in drive and drive in a circle until the bar quits flashing. Now get back on the road and get above 13 mph. Your temp gauge should now be working properly again since you just reset the sensor.
If it is not, then check the sensor connections. If that does not work, the sensor needs to be replaced. "