DTC P0128-00: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature); DTC P0128-07: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) Mechanical Failure [11/2023 - ]: Procedure

1. Read the DTCs.

   Powertrain > Engine > Trouble Codes 

   Result

   Result	Proceed to
   DTC P0128-00 or P0128-07 is output	A
   DTC P0128-00, P0128-07 and other DTCs are output	B

   HINT: 

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

Result: 

B 

GO TO DTC CHART  . Refer to DIAGNOSTIC TROUBLE CODE CHART [11/2023 - 11/2024] , or refer to DIAGNOSTIC TROUBLE CODE CHART [11/2024 - ]

Result: 

A 

See step  2

1. Check for defects in the engine cooling system that might cause the system to be excessively 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 [10/2021 - ]

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPLACE WATER INLET WITH THERMOSTAT SUB-ASSEMBLY 

Refer to REMOVAL [10/2021 - ]

Result: 

OK 

See step  4

Refer to INSPECTION [10/2022 - ]

HINT: 

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

Refer to INITIALIZATION [10/2021 - ]

Result

Result: 

NG 

REPLACE ENGINE COOLANT TEMPERATURE SENSOR 

Refer to REMOVAL [11/2023 - ]

Result: 

OK 

See step  5

Refer to PROCEDURE - Step 2

Result

Result: 

OK 

REPLACE ECM 

Refer to REMOVAL [11/2023 - ]

Result: 

NG 

REPLACE NO. 2 ENGINE COOLANT TEMPERATURE SENSOR 

Refer to PROCEDURE - Step 2