Actually, there are two coolant temperature sensors. One is for the gauge and the other tells the ECM [computer] what the coolant temperature is. If your gauge is reading normal, that sensor is probably OK. It is likely the other sensor is giving false info to the ECM which is turning on the light and showing a code P0128. If it is sending a reading that is too low, the ECM demands more fuel from the injectors [usually resulting in poor fuel mileage]. If it is sending a reading that is too high [overheating] the ECM says to lean out the fuel mixture. The vehicle would then be very difficult to start and drive when cold until completely warmed up. False readings somewhere in the middle will give combinations of both symptoms.
Good answer, interesting point. I'd just add that the basic meaning for a P0128 code is:
Coolant Thermostat Problem. Usually not getting hot enough in the time given, that is standard.
P0105 is MAP (Manifold Absolute Pressure) or BARO (Barometric pressure) circuit malfunction.
P0120 is TPS (Throttle Position Sensor) circuit malfunction.
trouble code p-0837 fo jeep liberty
This code is defined as: Output Speed Sensor Circuit
Trouble code P0442 means: Evaporative Emission System Leak Detected (small leak)
Trouble code P0404 means:Exhaust gas recirculation circuit range/performance
Trouble code P0103 means:Mass or volume circuit high input
Trouble code P0128 means: ECT Sensor Below Thermostat Regulating Temperature
Trouble code P0128 means: ECT Sensor Below Thermostat Regulating Temperature
Trouble code P0128 means:Coolant thermostat (coolant temp below thermostat regulating temp)
Trouble code P0128 means: ECT Sensor Below Thermostat Regulating Temperature
Start with replacing the thermostat.
Trouble code P0128 means:Coolant thermostat (coolant temp below thermostat regulating temp)
Trouble code P0128 means:Coolant thermostat (coolant temp below thermostat regulating temp)
Trouble code P0128 means:Coolant thermostat (coolant temp below thermostat regulating temp)
Trouble code P0128 means:Coolant thermostat (coolant temp below thermostat regulating temp)
Trouble code P0128 means: ECT Sensor Below Thermostat Regulating Temperature
Trouble code P0128 means:Coolant thermostat (coolant temp below thermostat regulating temp)
Trouble code P0128 means:Coolant thermostat (coolant temp below thermostat regulating temp)