Temperature Gauge Malfunctions

Sounds like a bad connection at the coolant temperature sensor. If your check engine light is on this will confirm my suspicion. When the coolant temperature sensor is unplugged and the computer is not receiving a signal from it the temperature gauge will go down to cold, the check engine light will come on, and the air conditioning will be disabled. If you have an electric radiator cooling fan that will come on at high speed too. Without a signal from the coolant temperature sensor the computer assumes that the engine is overheating and does the above mentioned things to prevent engine damage. So check the wiring going to the coolant temperature sensor. If the wiring is good, replace the sensor. Get a Delco sensor. For some reason GMs don't like aftermarket coolant temperature sensors. Hope that helps! Jim