DTC P0128-00: Thermostat monitor

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 900 seconds.

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 240 seconds has passed.

FAIL-SAFE AND BACKUP FUNCTION

None.

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function, OBD-II Drive Cycle – Pattern 3 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

Required Special Tools:

MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
MB992745: V.C.I.-Lite main harness A
MB992747: V.C.I.-Lite USB cable short
MB992748: V.C.I.-Lite USB cable long

1.STEP 1. Check the engine cooling system.

Check the engine cooling system (Refer to ENGINE, Engine Cooling –Engine Cooling Diagnosis – Symptom Chart SYMPTOM CHART

Is the engine cooling system normal?

Repair it. Then

2.STEP 2. Test the OBD-II drive cycle.

After erasing the DTC, carry out test drive with the drive cycle pattern, and recheck the DTC.

(1) Use scan tool (M.U.T.-III SE) to erase the DTC.

(2) Carry out test drive with the drive cycle pattern (Refer to Diagnostic Function, OBD-II Drive Cycle – Pattern 3 OBD- II DRIVE CYCLE

(3) Use scan tool (M.U.T.-III SE) to recheck the DTC.

Q: Is DTC P0128-00 set?

Replace the ECM (Refer to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION

Intermittent malfunction (Refer to GENERAL INFORMATION, General Information – How to Use Troubleshooting/Inspection Service Points – How to Cope with Intermittent Malfunctions HOW TO COPE WITH INTERMITTENT MALFUNCTIONS