P0128

DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

TECHNICAL DESCRIPTION
- The PCM 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)
- 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 15 g/sec be within 300 seconds.

Judgment Criteria
- The time for the engine coolant temperature to rise to 77 °C (171 °F) takes longer than approximately 7 to 16 minutes
- The PCM monitors for this condition once during the drive cycle.

OBD-II DRIVE CYCLE PATTERN
None

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

DIAGNOSIS

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

Q: Is the cooling system normal?

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

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