Just changed my thermostat to a higher degree. Now my engine light is on the code says..COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE CODE P0128

code p 0128 refers to coolant thermostat --coolant temp below thermostat regulating temperature ===causes--- mechanical fault
remove and test the thermostat --replace if necessary
It may be stuck open and not regulating coolant flow there by not allowing the engine to come to operating temperature

Trouble Code: P0128

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Possible Causes:


Insufficient warm-up time.Low engine coolant level.Leaking or stuck open thermostat.Inoperative engine coolant temperature sensor.Inoperative cylinder head temperature sensor.Here are the reasons.

Well, I can't give you any specific information regarding your vehicle because you forgot to mention what kind of vehicle you have. (This is kinda important if you really want some help figuring out what is wrong with your car)

The "Generic OBD" of code P0128 is "Coolant Temperature Below Thermostat Regulating Temperature"

The most likely cause is a stuck-open thermostat, however, I have also seen defective Engine Coolant Temperature (ECT) sensors also cause this code.

it is caused by a bad thermostat, if it still does this. change coolant tempurature sensor. have a good day !

P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.

Symptoms: You will likely not notice any drivability problems other than the MIL illumination.

Causes: A code P0128 may mean that one or more of the following has happened:
* Low engine coolant level
* Leaking or stuck open thermostat
* Faulty cooling fan (running too much)
* Faulty coolant temperature (ECT) sensor
* Faulty intake air temperature (IAT) sensor

Possible Solutions: Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:
* Verify coolant strength & level
* Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
* Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
* Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
* If the above items check out good, replace the thermostat
* If Nissan vehicle, check for Technical Service Bulletins (TSBs), as the ECM may need to be reprogrammed to correct the P0128 code

Hope helps (remember to rate and comment this).

CODE P0128- THERMOSTAT MALFUNCTION. POSSIBLE CAUSES 1. ECT SENSOR IS OUT OF CALIBRATION. 2. CHECK THE OPERATION OF THE THERMOSTAT IT MAY BE STUCK OPEN.3.INSPECT FOR LOW COOLANT LEVEL OR FOR AN INCORRECT COOLANT MIXTURE.

Trouble Code: P0128

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Possible Causes:


Insufficient warm up time Low engine coolant level Leaking or stuck open thermostat Inoperative engine coolant temperature (ECT) sensor Inoperative Cylinder Head Temperature (CHT) sensor

P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

P0410 - Secondary Air Injection System Malfunction
(has to do with exhaust system)

Note: There is a technical service bulletin (TSB) regarding code P0410 for a number of GM models. The TSB calls for the replacement of the AIR pump and the installation of a new secondary injection hose.

P0128 - Coolant Thermostat Below Thermostat Regulating Temperature
REPLACE THE THERMOSTAT THE ENGINE IS NOT REACHING CORRECT OPERATING TEMPERATURE, 190-195 DEGREE'S FAHRENHEIT.