P0128
DTC P0128 THERMOSTAT FUNCTIONOn Board Diagnosis Logic
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
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 52 °C (126 °F).
- Before performing the following procedure, do not fill with the fuel.
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 that the "COOLAN TEMP/S" is above 52 °C (126 °F).
If it is below 52 °C (126 °F), go to following step.
If it is above 52 °C (126 °F), cool down the engine to less than 52 °C (126 °F). Then go to next steps.
6. Start engine and let it idle for at least 30 minutes.
If "COOLAN TEMP/S" increases to more than 71 °C (160 °F) within 30 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 "Diagnosis Procedure".
WITH GST
1. Follow the procedure "WITH CONSULT-III" 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.
2. If NG, replace engine coolant temperature sensor.