P0128

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

TECHNICAL DESCRIPTION
- The ECM [M/T] or the PCM [A/T] 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)
- 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:

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 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 over 10 g/sec within 600 seconds.

Judgement Criterion
- The time for the engine coolant temperature to rise to 77 °C (171 °F) takes longer than approximately 11 to 32 minutes.

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

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- The thermostat is faulty.
- ECM failed. [M/T]
- PCM failed. [A/T]

DIAGNOSIS

STEP 1. Check the cooling system.

Refer to Engine Cooling Diagnosis.

Q: Is the cooling system normal?

YES : Replace the ECM or the PCM. When the ECM or the PCM is replaced, register the encrypted 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 10. 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.