I replaced my coolant temperature sensor because it was running cold. After replacing it the temperature Gage went immediately to the hot position and began to overheat.

What diognostics say its a sensor ?????? No diagnostic's ever tell's you it's a sensor . You as a technician would need to prove that by testing electrical circuits , viewing coolant temp sensor . Hooking scan tool and trying to command the gauge with by directional control . The temp gauge not showing any temp. ? No movement ? Engine Coolant Temperature Gage Inaccurate or InoperativeStep Action
Yes
No
Schematic Reference: Instrument Cluster Schematics
1
Did you perform the Instrument Cluster Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - Instrument Cluster
2
Install a scan tool.
Turn the ignition ON, with the engine OFF.
With the scan tool, perform the Lamp and Gauge Check in the IPC Special Functions list.
Does the engine coolant temperature gage move up and down when commanded?
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
Go to Step 3
3
Replace the IPC. Refer to Instrument Cluster Replacement .
Did you complete the replacement?
Go to Step 4
--
4
Operate the system in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 2
Would hate for you to replace the coolant temp sensor an find out that's not the problem ! Does the vehicle start an run good ,trans mission shift good ? If so it's not the coolant temp sensor .
Engine Coolant Temperature Gage
The ECM sends coolant temperature as determined by the coolant temperature sensor to the BCM via CAN serial data. The IPC displays the engine coolant temperature with the gage when the BCM sends a class 2 message to the IPC indicating coolant temperature percentage. The engine coolant temperature gage defaults to cold (0°) or below if:
• The ECM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of class 2 communications with the BCM.
• The BCM detects a loss of CAN communications with the ECM.

Do you have a temperature gage in your instrument cluster? When the temp goes cold, does the temp gage rise? Check your coolant level both in the radiator and the coolant recovery tank under the hood, and fill as necessary. If that is OK, then check your serpentine belt for wear and/or slippage around the water pump. Lastly, if you have a temp gage and are noticing fluctuations in the reading, you may need to replace your cooling system thermostat. Good luck.

Sounds like your cooling fans on the radiator are not working. The fans are activated by a thermol switch on the engine or radiator reading the coolant temperature and an A/C switch. When the coolant is too hot the fans should activate cooling the system down. And, when the A/C is on the fans should also activate in order to cool the condensate so the A/C would work.

When you are driving, the movement of the vehicle throught he air is providing enough air flow to keep things cool and functional.

I would check the radiator fan fuse or fuses first. If those are OK I would try to run the fans with 12 volts and a ground that I supply just to see if the fan motor(s) actually run when powered. If the fan don't run when powered then the fans are bad and will need to be replaced. If the fans do run when you power them manually, then something is not allowing the power to activate, like a relay, control unit, or wiring.

It will take a little diagnostics, but it is not too difficult to chase it down.

Did you replace the thermostat? If it's bad your engine could be running cold, not letting the coolant get hot enough to get proper heat AND making your temperature gauge read cold.

Either the sensor is faulty (not uncommon) or the wire to the sensor has been damaged and is earthing to the bodywork.

To check, disconnect the wire connector at the sensor. If the temp gauge stays high then there's a wiring fault. If not just change the sensor. You'll have to partially drain the coolant to do so so make sure you release the pressure cap first and catch the drained coolant in a clean container for re-use. If the coolant is any colour other than a definite blue or pink then discard the drained coolant and top up with fresh coolant mix. Turn the heater in the car to cold before draining dow: this keeps the coolant in the heater core and prevents air locks when you refill the system. Also, the new sensor should come with a new seal. If not then order a new seal when you order the sensor.

I hope that I've been of assistance and that you soon resolve your problem. Don't put it off, as a simple £5 sensor protects you from a potential four figure repair bill.

Could be the coolant temperature sending sensor , the circuit the gauge, incorrect coolant mix , water pump, defective radiator or the vehicle could be running hot.Have the vehicle checked out by a repair shop.

the first thing is to check the coolant level, if coolant is full you may have a bad thermostat or a bad coolant temp sensor,when it runs hot, the best way to determine if it is hot is to check the temp at the sensor with temp checking tool.

The problem is almost for sure the guage, replace it.

yes inexpensive and easy to change located on the engine block is a two wire sensor threaded into the water jacket, you should also check to see if your heater hoses (both) are hot after 20 min of idling if they are cold you should check your coolant and the lower radiator hose to see if its cold as well if so you thermostat need to be replaced, as for the ac may need a charge ?does this truck have electronic climate control? also how does the temp gage on the dash read while driving ? please rate -jeff