I have a 2005 pontiac sunfire the car is exceeding normal level temperture to 90

Check fluid level and add if needed if not low would drain fluid and replace fluid filter and gaskets in pan.

You will have to change the whole dash unit from the sound of it ,its a mini computer behind it

It should fall between 200 and 250 degrees F, I take it when you say 90, that means 90 degrees Celsius, that equates to 194 degrees F.

You are within range, actually running little bit cooler, which is GREAT!

Check fluid level of hydraulic clutch that would cause this condition if low in fluid or not bled of air.

that could be a relay switch,look under the hood for a rectangled shape black box the relays should be located in that box

filler plug on the side of gearbox under neath

ground problem check connections or a fuse

what exceeds to 90 degrees?
The normal coolant temp will be over 190 degrees just from the thermostat in the engines,it will kick the cooling fans on at 210 degrees,

coolant temperture sensoris most likely your issue but before buying this part and installing, i would check all fuses and relays first.

I assume this is an automatic transmission, you didn't say.
There is no dip stick on the transmission any longer.
You will have to go under the car to check. You may want to go to your local instant oil change and have them check the level.
If you feel you want to check it, here is a description of the location and process.

Make certain the vehicle remains level while checking the fluid.
Located just above the top sealing flange of the transmission oil pan you will find a threaded plug. Remove the plug and see if transmission fluid drips out of the hole. If so, the fluid level is correct. If not, remove the red fill cap on top of the transmission, driver side. Add fluid to the transmission until fluid dribbles out of hole.
Replace and tighten the plug.
Good luck.
Regards,