Temperature gauge when ignition switched on temperature gauge goes to hot although engine cold

Has CHT - cylinder head temp. sensor . This sensor is a input to the PCM - engine computer . The PCM sends engine temp info on serial data network to the instrument cluster . I/C has a microprocessor inside . Have it check for DTC'S - diagnostic trouble codes . Not OBD2 codes , B - body codes . The gauge could be the problem , which means replacing the instrument cluster .
Engine coolant temperature information is received by the instrument cluster from the PCM over the SCP network. Temperatures over 121°C (275°F) will display hot (H). If the engine coolant temperature data is missing or invalid for five seconds, the instrument cluster will move the engine coolant temperature gauge below the cold (C) position.
The best way to diagnose this is with a scan tool , factory or a professional type . Know how the system works and not replacing parts is the proper way to diagnose .
U1073 D073 SCP (J1850) Invalid or Missing Data for Engine Coolant PCM CARRY OUT the PCM self-test.

• A single gauge does not return to zero with the ignition switch off

• Instrument cluster.

• INSTALL a new instrument cluster; REFER to Instrument Cluster . TEST the system for normal operation.

• Incorrect temperature gauge indication

• Circuitry.
• Instrument cluster.
• PCM.
• Engine coolant temperature sensor.

• GO to Pinpoint Test F .

I should also point out that if the temp sensor were bad the vehicle may not run right .
Using the factory scan tool
Trigger instrument cluster active command ENGCOOLNT. Monitor the engine coolant temperature gauge while adjusting the ENGCOOLNT active command to read 50% and 100%.

• Does the temperature gauge start at cold, move to half at 50%, and full hot at 100%?

Yes REFER to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.

No INSTALL a new instrument cluster; REFER to Instrument Cluster . REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
Your best bet , take it to a qualified repair shop !

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This is a tough one something like this should be handled with a diagnostic tool. Seeing that your temperature gauge is pined when the engine is cold, your temperature sender could be sending false readings back to the computer, although your engine is equipped with the separate temperature sender for the engine control module. I once repaired a problem with the ignition coil, it would fail when hot, and start working again when it cooled down. This solution is really shot in the dark, I would pick up a diagnostic reader, they're not that expensive. GOOD LUCK

check that the wire to the temp sender unit has not fallen off and is shorting out on the head/block. The power comes from the ignition switch through the gauge down to the sender unit and because the sender is a temperature controlled resistance unit the voltage is very low and so the gauge reads cold . as the temperature heats up , the resistance is decreased and so the voltage is increased though the gauge and the needle reads higher.. Hench if the gauge goes directly to hot on start up the wire is shorting out or the sender unit is faulty.

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These details will help.
Thanks.

YOur guage is faulty. Your will need to replace your guage if it stays in the hot position even when your car is off and your key is out of the ignition. If it only rises to hot when you turn the key to the run position, you have a wire between your guage and your temp sending unit that has been gounded out. Usually this happens when a person opens their hood to add oil or perform some minor maintenance on the engine and inadvertantly bumps the sensor or switch or wiring. This causes about 65% of these minor issues people incur, but if it does stay all the way up with your key out of the ignition switch, then you will need to replace your temp guage.

Either the temperature gauge switch is bad or you have air in your cooling system.

if the gauge goes straight to half, even when the engine is stone cold, i would suspect a bad temperature gauge sending unit. you will find it near the thermostat housing. good luck!

Here's the thing. The ECU will shut down AC if the engine temperature is too hot. If the coolant temperature sensor is malfunctioning (lying to the ECU) telling it that the temperature is hotter than it actually is, the computer will turn the AC OFF.

The guage and fan speeds work on independant sensors. If you can remove the plastic engine cover and locate the "sending unit" for the gauge disconnect it and restart the engine. The gauge should remain cold and not move. If this is the case replace the sending unit. This should be a single wire sender located in the waterjacket of the intake manifold look in the area where the upper rad hose enters the intake.