Trouble Codes

P0128 – Coolant Temperature Below Thermostat Regulating Temperature

Description of the DTC code P0128 Generic
Diagnostic code P0128 OBD II indicates that the PCM (Powertrain Control Module) has detected that the motor has not reached the expected temperature within a specific period of time after starting the motor. To give this determination, it is based on the amount of time the vehicle has been in operation, on the reading of the IAT sensor (Intake Air Temperature), on the reading of the ECT sensor (Engine Coolant Temperature) and on the vehicle speed.

Symptoms of the DTC code P0128 Generic
The service light on the check engine board lights up.

Causes of DTC code P0128 Generic
A code P0128 can be caused by one or more of the following problems:

  • The thermostat may be stuck leaky.
  • There is a low level of engine coolant.
  • The warm-up time is not enough.
  • The Coolant Temperature Sensor (ECT) may be defective.
  • The ECT (Engine Coolant Temperature) cable system can be short.
  • There is a bad electrical connection in the ECT sensor circuit.

Possible solutions of the DTC code P0128 Generic
To fix the DTC code P0128 you can check the following components:

  • Check the resistance and coolant level.
  • Make sure the cooling fan works correctly because it can run more than it should. Change it if necessary.
  • The temperature of the ECT sensor must be within the correct parameters, replace if necessary.
  • Check that the temperature of the Input Air Temperature Sensor (IAT) is OK. You can change it if necessary.
  • Change the thermostat.