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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 set in memory for the item monitored below)
  • Vehicle speed sensor 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
 
 
Check Conditions
  • Engine coolant temperature is between -10°C (14°F) and 57°C (140°F) when the first time 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 first time engine is started is 10°C (18°F) or less.
  • The total time when the amount of intake air is small is less than the specified time.
Judgment 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 3 .
 
 
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 GROUP 14A, Engine Cooling Diagnosis - Symptom Chart .
Is the cooling system normal?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 2.
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 3 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0128 set?
Retry the troubleshooting.
The inspection is complete.