It could be the temp sensor? Go to this site: http://www.ncttora.com/fsm/index.html
and you can down load the FSM. It will help you out in the future.
Go about half way down the page to Engine coolant temp sensor area. All the pictures and info you need. Even inspection page.
My temp gauge is not working on my '01 Tacoma 3.4L V6. I just replaced the coolant sensor last night and it still does not work. Is there something else that can be causing this? I read in the Hayes manual that it could be a fuse, but it didn't mention which one.
First suspect is the connection to the temp sensor for the temp gauge. It uses a separate sensor from the one the ECU uses. The one for the gauge is at the rear of the engine one top just forward of the heater control valve. Just look for the heater hoses, then down and a little forward and look for the sensor wire. Maybe the connector has some corrosion or other crap on it or has become disconnected.
Current flow is from the 10A gauge fuse, through the temp gauge meter movement, then through a series resistor, out the gauge cluster ribbon connector, through the wiring harness with the ECU wiring, then to the sensor and to ground. The sensor is a thermistor so its resistance varies with temperature. Since the 10A gauge fuse powers a lot of other stuff, I doubt it's the fuse. Thermistor are fairly simple so they rarely fail, connectors are more likely to cause your problem. The one for the temp sensor itself is exposed to more crap like oil, dirt, vibration and temperature extremes so go after that one first.
Mine is intermittent but to get at it for a decent clean up, I'd have to remove the blower and it not worth doing that just to fix that connection. Once in while, I reach up under there the best I can and try to give it a wiggle. It lasts for a while then gets dicey again.