DTC P0128-00: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature); DTC P0128-07: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) Mechanical Failure [08/2020 - 12/2021]: 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 / Trouble Codes.
5. Read the DTCs.

   Powertrain > Engine > Trouble Codes 

   Result

   Result	Proceed to
   DTC P0128-00 is output	A
   DTC P0128-07 is output (w/ Grille Shutter System)
   DTC P0128-07 is output (w/o Grille Shutter System)	B
   DTC P0128-00, P0128-07 and other DTCs are output	C

   HINT: 

   If any DTCs other than P0128-00 or P0128-07 are output, troubleshoot those DTCs first.

Result: 

B 

See step  6

Result: 

C 

GO TO DTC CHART 

Refer to DIAGNOSTIC TROUBLE CODE CHART [08/2020 - 12/2021]

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 ENGINE COOLING SYSTEM 

Result: 

OK 

See step  3

1. Inspect the water inlet with thermostat sub-assembly (thermostat opening temperature).

   Refer to INSPECTION [11/2018 - ]

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPLACE WATER INLET WITH THERMOSTAT SUB-ASSEMBLY 

Refer to REMOVAL [08/2020 - 10/2022]

Result: 

OK 

See step  4

1. Inspect the engine coolant temperature sensor.

   Refer to INSPECTION [11/2018 - ]

   HINT: 

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

   Refer to INITIALIZATION [08/2020 - 12/2021]

   Result

   Result	Proceed to
   OK (w/ Grille Shutter System)	A
   OK (w/o Grille Shutter System)	B
   NG	C

Result: 

B 

REPLACE ECM 

Refer to REMOVAL [08/2020 - 10/2022]

Result: 

C 

REPLACE ENGINE COOLANT TEMPERATURE SENSOR 

Refer to REMOVAL [08/2020 - ]

Result: 

A 

See step  5

1. Inspect the No. 2 engine coolant temperature sensor.

   Refer to PROCEDURE - Step 2

   Result

   Proceed to
   OK
   NG

Result: 

OK 

REPLACE ECM 

Refer to REMOVAL [08/2020 - 10/2022]

Result: 

NG 

REPLACE NO. 2 ENGINE COOLANT TEMPERATURE SENSOR 

Refer to REMOVAL [08/2020 - ]

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Enter the following menus: Powertrain / Transmission / Trouble Codes.
4. Check for DTCs.

   Powertrain > Transmission > Trouble Codes 

   HINT: 

   If DTCs related to the ATF temperature are output, troubleshoot those DTCs first.

   Result

   Result	Proceed to
   No DTCs are output.	A
   DTCs are output.	B

Result: 

B 

GO TO DTC CHART (AUTOMATIC TRANSAXLE SYSTEM) 

• for 2WD:

  Refer to DIAGNOSTIC TROUBLE CODE CHART [08/2020 - 12/2021]

• for AWD:

  Refer to DIAGNOSTIC TROUBLE CODE CHART [08/2020 - 12/2021]

Result: 

A 

See step  7

1. Cool the engine.
2. Connect the Techstream to the DLC3.
3. Turn the ignition switch to ON.
4. Turn the Techstream on.
5. Enter the following menus: Powertrain / Engine / Active Test / Activate the Coolant Water Route Switching Valve / Data List / Engine Speed and Coolant Water Route Switching Valve.

   Powertrain > Engine > Active Test 

   Active Test Display
   Activate the Coolant Water Route Switching Valve

   Data List Display
   Engine Speed
   Coolant Water Route Switching Valve

6. Perform the Active Test to close the flow shutting valve (for Heater Control).
7. Start the engine.
8. With the vehicle stationary, depress the accelerator pedal and maintain an engine speed of 1500 rpm for 15 seconds.
9. During the engine warm-up process, touch the flow shutting valve (for Heater Control) outlet and inlet hoses and check if there is a difference in temperature.

   OK

   There is a difference in temperature.

   HINT: 

   • P0128-07 may also be output if the flow shutting valve (for Heater Control) cannot fully close while the engine is cool.
   • If the flow shutting valve (for Heater Control) is closed during the engine warm-up process, there will be a difference in temperature between the outlet and inlet hoses.

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPLACE FLOW SHUTTING VALVE (FOR HEATER CONTROL) (WATER BY-PASS HOSE ASSEMBLY) 

Refer to REMOVAL [08/2020 - 10/2022]

Result: 

OK 

See step  8

1. Cool the engine.
2. Connect the Techstream to the DLC3.
3. Turn the ignition switch to ON.
4. Turn the Techstream on.
5. Enter the following menus: Powertrain / Engine / Active Test / Activate the Coolant Water Route Switching Valve 2 / Data List / Engine Speed and Coolant Water Route Switching Valve 2.

   Powertrain > Engine > Active Test 

   Active Test Display
   Activate the Coolant Water Route Switching Valve 2

   Data List Display
   Engine Speed
   Coolant Water Route Switching Valve 2

6. Perform the Active Test to close the flow shutting valve (for ATF Control).
7. Start the engine.
8. With the vehicle stationary, depress the accelerator pedal and maintain an engine speed of 1500 rpm for 15 seconds.
9. During the engine warm-up process, touch the flow shutting valve (for ATF Control) outlet and inlet hoses and check if there is a difference in temperature.

   OK

   There is a difference in temperature.

   HINT: 

   • P0128-07 may also be output if the flow shutting valve (for ATF Control) cannot fully close while the engine is cool.
   • If the flow shutting valve (for ATF Control) is closed during the engine warm-up process, there will be a difference in temperature between the outlet and inlet hoses.

   Result

   Proceed to
   OK
   NG

Result: 

OK 

See step  2

Result: 

NG 

REPLACE FLOW SHUTTING VALVE (FOR ATF CONTROL) (NO. 1 WATER BY-PASS HOSE) 

Refer to REMOVAL [08/2020 - 10/2022]