DTC P0128: Thermostat [03/2019 - 11/2022]: Procedure

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
5. Read the DTCs.

   Powertrain > Engine and ECT > Trouble Codes 

   Result

   Result	Proceed to
   DTC P0128 is output	A
   DTC P0128 and other DTCs are output	B

   HINT: 

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

Result: 

B 

GO TO DTC CHART 

Refer to DIAGNOSTIC TROUBLE CODE CHART [03/2019 - 04/2020] , or refer to DIAGNOSTIC TROUBLE CODE CHART [04/2020 - 09/2022] , or refer to DIAGNOSTIC TROUBLE CODE CHART [09/2022 - 11/2022]

Result: 

A 

See step  2

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

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE COOLING SYSTEM 

Result: 

OK 

See step  3

1. Inspect the thermostat (thermostat opening temperature).

   Refer to INSPECTION [01/2019 - 11/2022]

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPLACE THERMOSTAT 

Refer to REMOVAL [01/2019 - 11/2022]

Result: 

OK 

See step  4

1. Inspect the engine coolant temperature sensor.

   Refer to INSPECTION [01/2019 - 11/2022]

   HINT: 

   Perform "Inspection After Repair" after replacing the engine coolant temperature sensor.

   Refer to INITIALIZATION [01/2019 - 11/2022]

   Result

   Proceed to
   OK
   NG

Result: 

OK 

REPLACE ECM 

Refer to REMOVAL [03/2019 - 09/2022] , or refer to REMOVAL [09/2022 - 11/2022]

Result: 

NG 

REPLACE ENGINE COOLANT TEMPERATURE SENSOR 

Refer to REMOVAL [03/2019 - 09/2022] , or refer to REMOVAL [09/2022 - 11/2022]