P0128

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 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)
- Mass 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 60 °C (140 °F) when the engine is started.
- Intake air temperature is -10 °C (14 °F) or higher 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 total time of the mass airflow sensor output whose state is below 10 g/sec within 400 seconds.

Judgement Criteria
- The time for the engine coolant temperature to rise to 77 °C (171 °F) takes longer than approximately 11 to 20 minutes.

OBD-II DRIVE CYCLE PATTERN
Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern. OBD-II Drive Cycle

TROUBLESHOOTING HINTS
(The most likely causes for this code to be set are:)
- The engine cooling system is faulty.
- ECM failed.

DIAGNOSIS

STEP 1. Check the cooling system.

Refer to Engine Cooling Diagnosis.

Q: Is the cooling system normal?

YES : Go to Step 2.

NO : Repair it. Then Go to Step 2.

STEP 2. Test the OBD-II drive cycle.

1. Carry out test drive with the drive cycle pattern. Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 10. OBD-II Drive Cycle
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0128 set?

YES : Replace the ECM. When the ECM is replaced,register the ID code. Refer to Diagnosis-ID Codes Registration Judgment Table [Vehicles with KOS] or Diagnosis-ID Codes Registration Judgment Table [Vehicles with WCM].

NO : It can be assumed that this malfunction is intermittent. Refer to General (Body and Chassis), How to Use Troubleshooting/Inspection Service Points How to Cope with Intermittent Malfunctions.