DTC P0128 [MZI-3.7 (PCM CONNECTOR (2 TYPES))]

id0102e3817300

DTC P0128

Coolant thermostat (coolant temp below thermostat regulating temperature)
DETECTION CONDITION
•  P0128 Indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.
POSSIBLE CAUSE
•  Insufficient warm up time
•  Low engine coolant level
•  Leaking or stuck open thermostat
•  Inoperative cylinder head temperature (CHT) sensor
•  PCM malfunction

Diagnostic procedure

STEP

INSPECTION

ACTION
1
VERIFY FREEZE FRAME DATA HAS BEEN RECORDED
•  Has FREEZE FRAME DATA been recorded?
Yes
Go to the next step.
No
Record FREEZE FRAME DATA on the repair order, then go to the next step.
2
VERIFY RELATED SERVICE INFORMATION AVAILABILITY
•  Verify related Service Information availability.
•  Is any related Service Information available?
Yes
Perform repair or diagnosis according to the available Service Information.
•  If the vehicle is not repaired, go to the next step.
No
Go to the next step.
3
INSPECT ENGINE COOLANT LEVEL
Warning
•  Never remove the cooling system cap or loosen the radiator drain plug while the engine is running, or when the engine and radiator are hot. Scalding engine coolant and steam may shoot out and cause serious injury. It may also damage the engine and cooling system.
•  Turn off the engine and wait until it is cool. Even then, be very careful when removing the cap. Wrap a thick cloth around it and slowly turn it counterclockwise to the first stop. Step back while the pressure escapes.
•  When you're sure all the pressure is gone, press down on the cap using the cloth, turn it, and remove it.
•  Is the engine coolant fill level correct?
Yes
Go to the next step.
No
Inspect for a loss of engine coolant. Repair if necessary.
(See ENGINE COOLANT LEVEL INSPECTION [MZI-3.7].)
Go to Step 5.
4
INSPECT SENSOR OPERATION
•  Run the engine until the engine temperature stabilizes.
•  Verify that the radiator hoses are hot and the cooling system is pressurized.
•  Access the PCM and monitor the CHT PID.
•  Is the temperature more than 77 °C {171 °F}?
Yes
The test is complete. Go to the next step.
No
Inspect the thermostat operation. Repair if necessary.
(See THERMOSTAT INSPECTION [MZI-3.7].)
5
VERIFY TROUBLESHOOTING OF DTC P0128 HAS BEEN COMPLETED
•  Verify that all disconnected connectors are reconnected.
•  Turn the ignition switch to the ON position (Engine off).
•  Clear the DTC from the PCM memory using the M-MDS.
•  Start the engine and run it at idle.
•  Retrieve DTCs using the M-MDS.
•  Is the PENDING CODE for this DTC present?
Yes
Replace PCM, then go to the next step.
(See PCM REMOVAL/INSTALLATION [MZI-3.7].)
No
Go to the next step.
6
VERIFY AFTER REPAIR PROCEDURE
•  Perform “AFTER REPAIR PROCEDURE”.
•  Are any DTC present?
Yes
Go to the applicable DTC inspection.
(See DTC TABLE [MZI-3.7 (PCM CONNECTOR (2 TYPES))].)
No
Troubleshooting completed.