P0128
DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)TECHNICAL DESCRIPTION
- The ECM
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)
- 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 degrees 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 total time of the mass airflow sensor output whose state is below 10 g/sec within 600 seconds.
Judgement Criteria
- The time for the engine coolant temperature to rise to 77 degrees C (171 degrees 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 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 or the PCM. When the ECM or the PCM is replaced, register the encrypted code. Refer to Encrypted Code Registration Criteria Table in Antitheft and Alarm Systems. 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.