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)

• Vehicle speed signal monitor
  

• 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 subtracted from the intake air temperature when the engine is started is lower than 10°C (18°F).
  
• The total time when the amount of intake air is small is less than the specified time.
  

• After the estimated engine coolant temperature rises above 77°C (171°F), the actual engine coolant temperature is less than 77°C (171°F) even though the specified time has passed.
  

FAIL-SAFE AND BACKUP FUNCTION

• None
  

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 9 .

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, ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, 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 9 .

	Retry the troubleshooting.

	The inspection is complete.