DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) [08/2015 - 10/2016]: Procedure

WARNING: This page is about a different car, the 2018 Toyota Sequoia, 2017 Toyota Sequoia, and 2016 Toyota Sequoia. However, it is still accessible from the selected car via links, so may be relevant.

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)

Connect the Techstream to the DLC3.
Turn the ignition switch to ON.
Turn the Techstream on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read DTCs.

RESULT

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

HINT:

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

Result:

GO TO DTC CHART

(Refer to DIAGNOSTIC TROUBLE CODE CHART [08/2015 - 10/2016] )

Result:

See step 2

CHECK COOLING SYSTEM
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.
Result:

NG

REPAIR OR REPLACE COOLING SYSTEM

Result:

OK

See step 3
INSPECT THERMOSTAT
1. Remove the thermostat (Refer to REMOVAL [08/2015 - 08/2018] ).
2. Measure the valve opening temperature of the thermostat.
  Standard opening temperature
  
  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 [08/2015 - 08/2018] ).
Result:

NG

REPLACE THERMOSTAT

(Refer to REMOVAL [08/2015 - 08/2018] )

Result:

OK

See step 4
INSPECT ENGINE COOLANT TEMPERATURE SENSOR
1. Inspect the engine coolant temperature sensor (Refer to INSPECTION [08/2015 - 08/2018] ).
  HINT:
  
  Perform "Inspection After Repair" after replacing the engine coolant temperature sensor (Refer to INITIALIZATION [08/2015 - 08/2017] ).
Result:

OK

REPLACE ECM

(Refer to REMOVAL [08/2015 - 08/2018] )

Result:

NG

REPLACE ENGINE COOLANT TEMPERATURE SENSOR