For California

P0128 THERMOSTAT FUNCTION





DTC Logic

DTC DETECTION LOGIC

NOTE:
If DTC P0128 is displayed with DTC P0300, P0301, P0302, P0303 or P0304, first perform the trouble diagnosis for DTC P0300, P0301, P0302, P0303, and P0304. Refer to For California.
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 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 -4�C (25�F) to 36�C (97�F).
- Before performing the following procedure, do not fill with the fuel.
- GO TO 2.
2.PERFORM DTC CONFIRMATION PROCEDURE
With CONSULT-III
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-III.
5. Check the indication of "COOLAN TEMP/S"
If it is below 36�C (97�F), go to following step.
If it is above 36�C (97�F), cool down the engine to less than 52�C (126�F). Then go to next steps.
6. Start engine and drive vehicle for 10 consecutive minutes under the following conditions.





If "COOLAN TEMP/S" increases to more than 71�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-III" above.
Is 1st trip DTC detected?
YES - Go to For California.
NO - INSPECTION END




Diagnosis Procedure
1.CHECK ENGINE COOLANT TEMPERATURE SENSOR
Refer to For California.
Is the inspection result normal?
YES - GO TO 2.
NO - Replace engine coolant temperature sensor.
2.CHECK THERMOSTAT
Refer to Service and Repair.
Is the inspection result normal?
YES - INSPECTION END
NO - Replace thermostat.




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.





4. Check resistance between engine coolant temperature sensor terminals as follows.





Is the inspection result normal?
YES - INSPECTION END
NO - Replace engine coolant temperature sensor.