Temperature gauge on the dash quit working on Pontiac Grand Prix?

Gauge quit working,its better chance,that there is air in coolant system.
Is the check engine light ON?

If yes,then there is definitely error code stored in system.

First try bleeding air in coolant system.
The bleeder should be in the top of the thermostat housing.

See the diagram shown below :-----








Low coolant can make the gage not read correctely , the check engine light can be cleared by removing the negative battery cable for about 10 minutes. If the light comes back on then you will need a code scan done because that means you still have a problem. Try bleeding it and clearing the code and see what happens. 

This details will help.

Thanks.

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