P0128

P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

TECHNICAL DESCRIPTION
- The ECM or PCM 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 air flow sensors output frequency is in the low frequency state for 465 seconds or less.

Judgment Criteria
- The time for the engine coolant temperature to rise to 77 °C (171 °F) takes longer than approximately 10 to 32 minutes.

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

DIAGNOSIS

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

Q: Is the cooling system normal?

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

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