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 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)

- Vehicle speed signal 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 60°C (140°F) when the 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 engine is started is lower than 10°C (18°F).
- The total time when the amount of intake air is small is less than the specified time.
Judgement 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 9 Monitors, Trips, Drive Cycles and Readiness Codes .

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.

Symptom Chart.

Q. Is the cooling system normal?

YES Replace the ECM (Refer to, Removal and Installation Removal and Replacement).
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 9 Monitors, Trips, Drive Cycles and Readiness Codes.

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0128 set?

YES Retry the troubleshooting.
NO The inspection is complete.