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.

DESCRIPTIONS OF MONITOR METHODS
- Engine coolant temperature does not reach 77 degrees C (171 degrees 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:

Logic Flow Chart

Check Conditions
- Engine coolant temperature is between -10 degree C (14 degrees F) and 77 degrees C (171 degrees F) when the engine is started.
- The engine coolant temperature - intake air temperature is 5 degrees C (41 degrees F) or less when the engine is started.
- The intake air temperature when the engine is started - intake air temperature is 5 degrees C (41 degrees 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 Criterion
- The time for the engine coolant temperature to rise to 77 degrees C (171 degrees F) takes longer than approximately 9 to 14.5 minutes.
- The ECM monitors for this condition once during the drive cycle.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 10. OBD-II Drive Cycle Pattern Lists

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 in Cooling System/Testing and Inspection

Q: Is the cooling system normal?

YES: Replace the ECM. Then go to Step 2.

NO: Repair it. Then go to Step 2.

STEP 2. Test the OBD-II drive cycle.

1. Carry out test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 10. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0128 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.