Radiator fan and temp gauge

Good morning. I am having issues with my cooling fan and temp gauge. I am thinking the issues are connected. First, I run the car to operating temp. I turn the motor off. Now when I turn the key to on but don't start, the temp gauge show about mid way. I start the car and the after about 5 seconds, the rad fan starts and the gauge drops to below cold. Even at cold start, the fan starts up after 5 seconds, but no gauge. I get a P1289 code. Could the cylinder head temp sensor cause this? There's no overheating issues. I can't see any wiring issues like splicing or cut wires. Thanks in advance guys.