Engine Controls

P0128 THERMOSTAT FUNCTION

DTC Logic


DTC DETECTION LOGIC

NOTE:
If DTC P0128 is displayed with DTC PP0300, P0301, P0302, P0303 or P0304, first perform the trouble diagnosis for DTC P0300, P0301, P0302, P0303, P0304. Refer to "DTC Logic" Engine Controls.
Engine coolant temperature has not risen enough to open the thermostat even though the engine has run long enough.
This is due to a leak in the seal or the thermostat stuck being open.






DTC CONFIRMATION PROCEDURE


1. PRECONDITIONING

If DTC CONFIRMATION PROCEDURE has been previously conducted, always turn ignition switch OFF and wait at least 10 seconds before conducting the next test.
TESTING CONDITION:
-For best results, perform at ambient temperature of -10�C (14�F) or higher.
-For best results, perform at engine coolant temperature of -10�C (14�F) to 56�C (133�F).
-Before performing the following procedure, do not add fuel.
- GO TO 2.

2. PERFORM DTC CONFIRMATION PROCEDURE

With CONSULT
1.Turn A/C switch OFF.
2.Turn blower fan switch OFF.
3.Turn ignition switch ON.
4.Select "COOLAN TEMP/S" in "DATA MONITOR" mode with CONSULT.
5.Check the indication of "COOLAN TEMP/S"
If it is below 56�C (133�F), go to next step.
If it is above 56�C (133�F), cool down the engine to less than 56�C (133�F). Then go to next steps.
6.Start engine drive vehicle for 10 consecutive minutes under the following conditions.






CAUTION:
Always drive vehicle at a safe speed.
NOTE:
If "COOLAN TEMP/S" increases to more than 75�C (160�F) within 10 minutes, turn ignition switch
OFF because the test result will be OK.
7.Check 1st trip DTC.
With GST
Follow the procedure "With CONSULT" above.
Is 1st trip DTC detected?
YES- Go to "Diagnosis Procedure" Engine Controls.
NO- INSPECTION END


Diagnosis Procedure


1. CHECK ENGINE COOLANT TEMPERATURE SENSOR

Refer to "Component Inspection" .
Is the inspection result normal?
YES- GO TO 2.
NO- Replace engine coolant temperature sensor. Refer to "Removal and Installation" Removal And Installation.

2. CHECK THERMOSTAT

Refer to "Removal and Installation" Removal And Installation.
Is the inspection result normal?
YES- INSPECTION END
NO- Replace thermostat. Refer to "Removal and Installation" Removal And Installation.


Component Inspection


1. CHECK ENGINE COOLANT TEMPERATURE SENSOR

1.Turn ignition switch OFF.
2.Disconnect engine coolant temperature sensor harness connector.
3.Remove engine coolant temperature sensor. Refer to "Removal and Installation" Removal And Installation.





4.Check resistance between engine coolant temperature sensor terminals by heating with hot water as shown in the figure.





Is the inspection result normal?
YES- INSPECTION END
NO- Replace engine coolant temperature sensor. Refer to
"Removal and Installation" Removal And Installation.