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

TECHNICAL DESCRIPTION

• The ECM checks the time for the cooling water temperature to reach the judgement 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)

• Not applicable
  

• Mass airflow sensor
  
• Engine coolant temperature sensor
  
• Intake air temperature sensor
  

DTC SET CONDITIONS

• Engine coolant temperature is between -10°C (14°F) and 60°C (140°F) when the engine is started.
  
• Intake air temperature is -10°C (14°F) or higher.
  
• The intake air temperature when the engine is started - intake air temperature is 5°C (9°F) or less.
  
• The total time of the mass airflow sensor output whose state is over 14 g/sec within 550 seconds.
  

• The time for the engine coolant temperature to rise to 77°C (171°F) takes longer than approximately 9.5 to 43.5 minutes.
  

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 10 .

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

• The engine cooling system is faulty.
  
• ECM failed.
  

Refer to GROUP 14, Engine Cooling Diagnosis .

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 2.

	Repair it. Then go to Step 2.

(1)Carry out test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 10 .

	Retry the troubleshooting.

	The inspection is complete.