DTC P0128: Coolant Thermostat Malfunction: Condition

DTC is set when engine coolant temperature is too low, less than 176°F (80°C), or too high 212°F (100°C) after engine has run for a specified time. Engine coolant temperature circuit is monitored once per drive cycle. MIL is illuminated when Engine Control Module (ECM) detects malfunction during 2 consecutive drive cycles. Possible causes are:

• Thermostat malfunction.
• ECT sensor malfunction.
• ECM malfunction.