DTC P0128-00: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature); DTC P0128-07: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) Mechanical Failure [11/2021 - 03/2022]: Procedure

1. Read the DTCs.

   Powertrain > Engine > Trouble Codes 

   Result

   Result	Proceed to
   DTC P0128-00 is output	A
   DTC P0128-07 is output	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  5

Result: 

C 

GO TO DTC CHART. Refer to  DIAGNOSTIC TROUBLE CODE CHART [11/2021 - 03/2022] 

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 ENGINE COOLING SYSTEM 

Result: 

OK 

See step  3

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

   Refer to INSPECTION [11/2021 - ]

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPLACE WATER INLET WITH THERMOSTAT SUB-ASSEMBLY. Refer to  REMOVAL [11/2021 - ] 

Result: 

OK 

See step  4

Refer to INSPECTION [11/2021 - ]

HINT: 

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

Refer to INITIALIZATION [11/2021 - ]

Result

Result: 

OK 

REPLACE ECM. Refer to  REMOVAL [11/2021 - ] 

Result: 

NG 

REPLACE ENGINE COOLANT TEMPERATURE SENSOR. Refer to  REMOVAL [11/2021 - ] 

1. 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
   DTCs are not output	A
   DTCs are output	B

Result: 

B 

GO TO DTC CHART (AUTOMATIC TRANSAXLE SYSTEM). Refer to  DIAGNOSTIC TROUBLE CODE CHART [11/2021 - 03/2024] 

Result: 

A 

See step  6

1. Cool the engine.
2. Perform the Active Test to close the flow shutting valve (for Heater Control).

   Powertrain > Engine > Active Test 

   Active Test Display
   Activate the Coolant Water Route Switching Valve

   Data List Display
   Engine Speed
   Coolant Water Route Switching Valve

3. Start the engine.
4. With the vehicle stationary, depress the accelerator pedal and maintain an engine speed of 1500 rpm for 15 seconds.
5. 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 [11/2021 - ] 

Result: 

OK 

See step  7

1. Cool the engine.
2. Perform the Active Test to close the flow shutting valve (for ATF Control).

   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

3. Start the engine.
4. With the vehicle stationary, depress the accelerator pedal and maintain an engine speed of 1500 rpm for 15 seconds.
5. 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 [11/2021 - ]