P0128

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

TECHNICAL DESCRIPTION
- The ECM checks the time for the cooling water temperature to reach the judgement 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)
- Vehicle speed signal monitor

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 60°C (140°F) when the engine is started.
- Intake air temperature is - 10°C (14°F) or higher.
- The intake air temperature subtracted from the intake air temperature when the engine is started is lower than 10°C (18°F).
- The total time when the amount of intake air is small is less than the specified time.

Judgement Criterion
- After the estimated engine coolant temperature rises above 77°C (171°F), the actual engine coolant temperature is less than 77°C (171°F) even though the specified time has passed.

FAIL-SAFE AND BACKUP FUNCTION
- None

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 9. OBD- II Drive Cycle

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

DIAGNOSIS

STEP 1. Check the cooling system.

Refer to Engine Cooling diagnosis. Symptom Related Diagnostic Procedures

Q: Is the cooling system normal?

YES : Replace the ECM. When the ECM is replaced, register the ID code. 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 9. OBD- II Drive Cycle
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0128 set?

YES : Retry the troubleshooting.

NO : The inspection is complete.