P0128
DTC P0128 : Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)TECHNICAL DESCRIPTION
- The ECM
DESCRIPTIONS OF MONITOR METHODS
- The thermostat is determined to be stuck open if the engine coolant temperature does not increase to 77 degrees C (171 degrees F) within a prescribed length of time after cold-starting the engine.
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
- Intake air temperature sensor
- Engine coolant 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 (9 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 (9 degrees F) or less.
- The volume airflow sensors output frequency is in the low frequency (50 - 100 Hz or less) state for 490 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 10 to 32 minutes.
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.
- PCM failed.
DIAGNOSIS
STEP 1. Check the cooling system.
Refer to Engine Cooling Diagnosis in Cooling System/Diagnostic Strategies.
Q: Is the cooling system normal?
YES: Replace the ECM
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.