My temperature gage not working on a 08 impala

It is possible that you have an airlock in the coolant system? That can cause symptoms of overheating and sometimes there isn't sufficient flow or the coolant temperature. The main tip is to turn the heater of full heat and also elevate the front of the vehicle.

https://www.fixya.com/cars/r29872074-vehicle_cooling_system_no_heat

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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.

My info shows two.
One is sender for gage on the dash.
the other, ect, tells the computer, the engine temp.
The sender for the temp gage has a one wire connector, red/white tracer.
The ect is a two wire connector, gray--gray with red tracer.
What kind of problem are you having?

I don't know if your the person I was talking to, but, you click on the comment link to reply.

Well it can be one of too things the gage or the temp sensor.
its most likely the sensor. The temp sensor is normally mounted with the thermostat housing which is on the top of the engine and has the top radiator hose going to it if you can't see it, try taking off the plastic covers. With the ignition on so all gages are reading go and unplug the sensor the gage should drop back strata way, this tells you that you have the wright sensor there are sometimes 2 one for the gage and the other for cold starting. There is a possibility that the problem may be coursed by a squashed or rubbed throw wire so if you can't make the gage return to cold by disconnecting the wires then start following the wires back along the engine.
I think you will find a faulty sensor is the cores of your problems and should be easy to pick up at any car part place.

These cars and their Monte Carlo cousins were notorious for wiring problems with the two wires coming off the temp sensor. Backtrack the wires for about the first 14" off the sensor and you will probably find a swell or a limp spot. When the computer loses this signal the computer doesn't the engine temp.

cooling temp sensor

have you checked to see if the cooling fan is working properly.if not then it will have to be checked to see if its the fan that is no good,wiring,or a relay.there are 2 temp sensors one for the gage/light and one for the computer to know what the engine temp is to alter engine controls and cooling fan operation.

if the engine is not over heating then the gage is in need of replacing.

Sounds like your temperature sending unit is bad. If you need instructions for replacing the sensor, please let us know.

-The radiator fan will be kick on ONLY when the temperature reach about 190-200. Depend on the sensor that you have now.
You can test it by boil it and hook up a digital multi meter to it.
and make sure use a temperature gage to test with, so you know how hot the water when it kick on.

Good luck
Mai