Originally Posted by 14Sport

This may help. It looks like you have to pull the left side inner fender liner to get to it on the 3.6.

Originally Posted by ronjenx

Perhaps this information will help you understand what the computer is looking for:

P0128-THERMOSTAT RATIONALITY

Theory of Operation


The PCM predicts what the engine coolant temperature should be, based on the engine coolant temperature at start-up, ambient temperature and how the vehicle is subsequently driven. The predicted engine coolant temperature is compared to the Engine Coolant Temperature Sensor reading. The error between the two is calculated and integrated with respect to time. When the Thermostat diagnostic runs, the integrated error is compared to a calibrated threshold and pass/fail is determined. Separate pass and fail thresholds are used in order to improve accuracy of the diagnostic.

• When Monitored: With the engine running, ambient temperature between -8° C (17.6° F) and 50° C (122° F), start up coolant temperature less than 50° C (122° F), and average vehicle speed greater than 16 kph (10 mph) until coolant temperature reaches 85° C (185° F).
• Set Condition: The PCM detects that the actual engine coolant temperature falls too far below the predicted engine coolant temperature and the predicted coolant temperature reaches the predicted target value before the actual coolant temperature reaches the actual coolant temperature target value. Two trip fault. Three good trips to turn off the MIL.

[TABLE]
[TR]
[TD="bgcolor: white"]Possible Causes
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]LOW COOLANT LEVEL
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]THERMOSTAT OPERATION
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]SIGNAL CIRCUIT SHORTED TO VOLTAGE
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]TEMPERATURE SENSOR
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]SIGNAL CIRCUIT OPEN
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]SENSOR GROUND CIRCUIT OPEN
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]SIGNAL CIRCUIT SHORTED TO GROUND
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]SIGNAL CIRCUIT SHORTED TO THE (K900), (G931) SENSOR GROUND CIRCUIT
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]OTHER POSSIBLE CAUSES
[/TD]
[/TR]
[TR]
[TD="bgcolor: white"]POWERTRAIN CONTROL MODULE (PCM)
[/TD]
[/TR]
[/TABLE]

NOTE: If any ECT, AAT, CMP or CKP sensor DTCs have set along with P0128, diagnose them before continuing.



NOTE: Make sure that the Pinion Factor has been programmed correctly into the PCM.



NOTE: Diagnose any CAN - C Communication DTCs before continuing.


NOTE: If an Engine Coolant Temperature (ECT) DTC is set along with this code, diagnose the ECT DTC first.



NOTE: Inspect the ECT terminals and related PCM terminals. Make sure the terminals are free from corrosion and damage.



NOTE: The best way to diagnose this DTC is to allow the vehicle to sit overnight outside in order to have a totally cold soaked engine.



NOTE: Extremely cold outside ambient temperatures may have caused this DTC to set.



WARNING: Never open the cooling system when the engine is hot. The system is under pressure. Failure to follow these instructions can result in personal injury including extreme burns, scalding, or death. Allow the engine to cool before opening the cooling system.

Originally Posted by jeepmojo

on doing this. it can be done with out removing any plastic. fender parts just pull the plastic on drivers side out and prop it with a wood block . you can then access the sensor. Be ready for a loss of coolant though. have some to replenish 50/50 distilled . Just get it in and screw it on as its coming out. i wouldnt wait for it to stop

Originally Posted by ZebraJacket99

Thanks for the tip! One question though, is there a torque/tightness called out on the sensor or just snug it up?