P0128
DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)TECHNICAL DESCRIPTION
- The ECM
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)
- 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:
Logic Flow Chart
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 total time of the mass airflow sensor output whose state is below 12 g/sec within 300 seconds.
Judgment Criteria
- The time for the engine coolant temperature to rise to 77 °C (171 °F) takes longer than approximately 11 to 12 minutes.
OBD-II DRIVE CYCLE PATTERN
None.
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.