Error Code P0128 - Thermostat or Temp Sensor

[klebmw]

Hi everyone, last week engine check wit error code P0128 and it likely Thermostat malfunction. I replaced new Mahle Thermostat on Monday and after 3 days driving, tonight the engine check and scanning error code P0128 again. I diagnostic and clear the code and restart the engine, the engine check light is gone.

However, the scanning tool software still show "PERMANENT" P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Is the new Thermostat defective? Is the Temperature Sensor fail? (I replaced genuine Temp sensor in January), i filled Coolant on Monday and rechecked coolant level is full.

(I attached the error image below)


Any help?

Thank you!