DTC P0128: Thermostat Rationality: Testing
WARNING:
Never open the cooling system when the engine is hot. The system is under pressure. Extreme burns or scalding may result. Allow the engine to cool before opening the cooling system.
Check the cooling system to make sure that the coolant is in good condition and at the proper level. If coolant level is low, check for visible leaks or perform a pressure test on the coolant system. Was the coolant level low or where any leaks found? If yes, repair the coolant leak and/or fill coolant to the proper level. If no, replace the thermostat and fill coolant level to the proper level.