P0128

DTC P0128: Coolant Thermostat Malfunction

TECHNICAL DESCRIPTION
- The ECM or PCM checks the time for the engine coolant 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)
- Volume 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 77° C (171° F) when the engine is started.
- The engine coolant temperature intake air temperature is 5° C (41° F) or less when the engine is started.
- The intake air temperature when the engine is started intake air temperature is 5° C (41° F) or less.
- The volume airflow sensors output frequency is in the low frequency (50 - 100 Hz or less) state for 300 seconds or less.

Judgment Criteria
- The time for the engine coolant temperature to rise to 77° C (171° F) takes longer than approximately 11 to 22 minutes.
- The ECM or 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
- ECU failed.
- PCM failed.

DIAGNOSIS

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

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.