Jeeps have coolant temperature sensors on the thermostat housing and on the top of the cylinder head on the driver's side of the engine. The second sensor is to the right of the valve cover. The front sensor has two wires and connects to the control module, while the second has one wire that connects to the dashboard indicator.
Most of the time, problems with the sensors are not with the unit itself, but the wiring that leads to it. Sometimes the wiring harness on older vehicles cracks and causes problems.
If the indicator light or temperature gauge is acting erratically, the problem is likely with the one-wire sensor. The control module uses readings from the back sensor to adjust the fuel-to-air ratio and the operation of the cooling fan. In some vehicles, the sensor switches on a diagnostic trouble code light when it fails. If the vehicle is running poorly and the diagnostic code indicates a temperature sensor, the two-wire sensor is the likely culprit.
Testing the two-wire sensor requires a thermometer, multimeter and method for adjusting the temperature of the sensor. If the sensor is operating correctly, the multimeter resistance reading should be within the manufacturer's specified range for the temperature. Units that read outside the range require replacement.