P0128

DTC P0128: COOLANT THERMOSTAT (COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE)

TECHNICAL DESCRIPTION
- The ECM checks the time for the engine coolant temperature to reach the judgment temperature.

DTC SET CONDITIONS

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 (50 - 100 Hz or less) state for 400 seconds or less.

Judgment Criteria
- The time for the engine coolant temperature to rise to 77 °C (171 °F) takes longer than approximately 9 to 14.5 minutes.
- The ECM monitors for this condition once during the drive cycle.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CODE TO BE SET ARE:)
- The thermostat is faulty
- ECM failed.

DIAGNOSIS

STEP 1. Check the cooling system.
Refer to Engine Cooling Diagnosis.

Q: Is the cooling system normal?

YES: Replace the ECM. Then check that the DTC P0128 does not reset.

NO: Repair it. Then check that the DTC P0128 does not reset.