Weird Temp Gauge

[Pearsons Diesel]

I just bought my wife an 03 explorer with the v8. Sometimes after its been driven for awhile it, the temp gauge will register hot as soon as it is switched back on. It has never run hot while being drove, it only does this after it is switched back on after sitting. It does go to half power and loses ac. Sometimes by turning the key on and off several times it will reset and it will run fine. The only code is a p1289. Thanks in advance for the help.

 

[Pearsons Diesel]

It did it again after we got home yesterday and with it running and the gauge pegged, I unplugged the sensor harness that comes out underneath the thermostat housing. The gauge dropped all the way down. I switched it off and plugged it back up and the it worked fine when I started it back up. Is this the coolant temp sensor. It is a round plug with 2 wires.

 

[jrford]

found this on a focus forum.

P1289 - Cylinder Head Temperature (CHT) Sensor Circuit High Input (PCM STRATEGIES 1999 AND BEYOND) Indicates a CHT sensor circuit malfunction (open). Open circuit in CHT harness
Damaged CHT sensor
Improper harness connection
Damaged PCM
CHT V PID reading greater than 4.6 volts with key ON and engine OFF or during any engine operating mode indicates a hard fault. Note: DTC P0118 may also be reported when this DTC is set, either of these DTC's will activate the MIL light.

 

[Pearsons Diesel]

Thank you. So it sounds like a bad sensor. Is this the one under the intake on the drivers side.