P0128 Coolant thermostat (Coolant temperature below thermostat regulating temperature)
Check Conditions
Engine coolant temperature is between −10°C (14°F) and 77°C (171°F) when the engine is started. The engine coolant temperature − intake air temperature is 5°C (9°F) or less when the engine is started. The intake air temperature when the engine is started − intake air temperature is 5°C (9°F) or less. The volume airflow sensors output frequency is in the low frequency state for 300 seconds or less.
Judgment Criteria
The time for the engine coolant temperature to rise to 77°C (171°F) takes longer than approximately 13 to 20 minutes. The PCM monitors for this condition once during the drive cycle.
- The thermostat is faulty.
- PCM failed.
Check Conditions
Engine coolant temperature is between −10°C (14°F) and 77°C (171°F) when the engine is started. The engine coolant temperature − intake air temperature is 5°C (9°F) or less when the engine is started. The intake air temperature when the engine is started − intake air temperature is 5°C (9°F) or less. The volume airflow sensors output frequency is in the low frequency state for 300 seconds or less.
Judgment Criteria
The time for the engine coolant temperature to rise to 77°C (171°F) takes longer than approximately 13 to 20 minutes. The PCM monitors for this condition once during the drive cycle.
- The thermostat is faulty.
- PCM failed.