DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

TECHNICAL DESCRIPTION
• The PCM checks the time for the cooling water temperature to reach the judgment temperature.
DESCRIPTIONS OF MONITOR METHODS
Engine coolant temperature does not reach 77°C (171°F) within specified period after cold start.
MONITOR EXECUTION
Once per driving cycle
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
• Not applicable

Sensor (The sensor below is determined to be normal)
• Volume airflow sensor
• Engine coolant temperature sensor
• Intake air temperature sensor
DTC SET CONDITIONS Logic Flow Chart


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 (50 - 100Hz or less) 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 12 to 20 minutes.
• The PCM monitors for this condition once during the drive cycle.
OBD-II DRIVE CYCLE PATTERN
None.
TROUBLESHOOTING HINTS
The most likely causes for this code to be set are:
The thermostat is faulty.
PCM failed.