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 judgment 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:
Logic Flow Chart
Check Conditions
Engine coolant temperature is between -10 °C (14 °F) and 77 °C (171 °F) when the engine is started.
The engine coolant temperature - intake air temperature is 5 °C (9 °F) or less when the engine is started.
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 below 15g/sec within 400 seconds.
Judgement Criteria
The time for the engine coolant temperature to rise to 77 °C (171 °F) takes longer than approximately 11 to 20 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 engine cooling system is faulty.
ECM failed.
DIAGNOSIS
STEP 1. Check the cooling system. Refer to Engine Cooling Diagnosis.
Q: Is the cooling system normal?
YES: 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: Replace the ECM. When the ECM is replaced, register the ID code. Refer to ID Code Registration Judgment Table
NO: It can be assumed that this malfunction is intermittent.