DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature): Procedure

1. Connect Techstream to the DLC3.
2. Turn the engine switch on (IG).
3. Turn the tester on.
4. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
5. Read the DTC.

   Result

   Display (DTC Output)	Proceed to
   P0128	A
   P0128 and other DTCs	B

   HINT: 

   If any DTC other than P0128 are output, troubleshoot those DTCs first.

B → GO TO DTC CHART 

A: Go to next step 

1. Check for defects in the cooling system that might cause the system to be too cold, such as abnormal radiator fan operation or any modifications.

NG → REPAIR OR REPLACE COOLING SYSTEM 

OK: Go to next step 

1. Remove the thermostat. Refer to REMOVAL .
2. Check the valve opening temperature of the thermostat.

   Standard

   80 to 84°C (176 to 183°F)

   HINT: 

   In addition to the above check, confirm that the valve is completely closed when the temperature is below the standard.

3. Reinstall the thermostat. Refer to INSTALLATION .

NG → REPLACE THERMOSTAT 

OK → REPLACE ECM