P0128

P0128 Thermostat Function

On Board Diagnosis 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, P0304. Refer to [P0300, P0301, P0302, P0303, P0304 Misfire]. 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.

P0128:

DTC Confirmation Procedure

With SDT

NOTE: 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.

1. Turn A/C switch OFF.
2. Turn blower fan switch OFF.
3. Turn ignition switch ON.
4. Select "COOLAN TEMP/S" in "Data list" mode with SDT.
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 and 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 (167 °F) within 10 minutes, turn ignition switch OFF because the test result will be OK.

7. Check 1st trip DTC.
8. If 1st trip DTC is detected, go to [P0128 Thermostat Function].

With GST
Follow the procedure With SDT above.

Diagnosis Procedure

Step 1-2:

Component Inspection

ENGINE COOLANT TEMPERATURE SENSOR
1. Check resistance between engine coolant temperature sensor terminals 1 and 2 as shown in the figure.






[Reference data]






2. If NG, replace engine coolant temperature sensor.