P0128

P0128 THERMOSTAT FUNCTION





DTC Logic

DTC DETECTION LOGIC

NOTE:
If DTC P0128 is displayed with DTC P0300, P0301, P0302, P0303, P0304, P0305 or P0306, first perform the trouble diagnosis for P0300, P0301, P0302, P0303, P0304, P0305, P0306. Refer to P0300.
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 being stuck open.






DTC CONFIRMATION PROCEDURE
1.PRECONDITIONING
If DTC Confirmation Procedure has been previously conducted, always perform the following before conducting the next test.
1. Turn ignition switch OFF and wait at least 10 seconds.
2. Turn ignition switch ON.
3. Turn ignition switch OFF and wait at least 10 seconds.
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
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 56�C (133�F), go to the next steps.
If it is above 56�C (133�F), cool engine down to less than 56�C (133�F). Then go to next step.
6. Start engine.
7. Drive vehicle for 10 consecutive minutes under the following condition.





If "COOLAN TEMP/S" increases to more than 75�C (167�F) within 10 minutes, turn ignition switch
OFF because the test result will be OK.

CAUTION:
Always drive vehicle at safe speed.
8. Check 1st trip DTC.
Is 1st trip DTC detected?
YES - Go to P0128.
NO - INSPECTION END




Diagnosis Procedure
1.CHECK ENGINE COOLANT TEMPERATURE SENSOR
Refer to P0128.
Is the inspection result normal?
YES - GO TO 2.
NO - Replace engine coolant temperature sensor.
2.CHECK THERMOSTAT
Check thermostat. Refer to Procedures.
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 by heating with hot water as shown in the figure.





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