DTC    P0128    Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

for Preparation Click here


DESCRIPTION

This DTC is set when the Engine Coolant Temperature (ECT) does not reach 75°C (167°F) despite sufficient engine warm-up time.

DTC No.
DTC Detection Condition
Trouble Area
P0128
  1. Conditions (a), (b) and (c) are met for 5 seconds (2 rip detection logic):
    1. Cold start
    2. Engine warmed up
    3. ECT less than 75°C (167°F)
  1. Thermostat
  2. Cooling system
  3. ECT sensor
  4. HV Control ECU

INSPECTION PROCEDURE

HINT:
Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was LEAN or RICH, and other data from the time the malfunction occurred.

1.CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0128)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the ignition switch ON.

  1. Turn the tester ON.

  1. Enter the following menus: Powertrain / Engine / DTC.

  1. Read the DTC.

    Result:

    Display (DTC Output)
    		Proceed to
    P0128
    		A
    P0128 and other DTCs
    		B

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



B
GO TO DTC CHART
A


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.



NG
REPAIR OR REPLACE COOLING SYSTEM
OK


3.INSPECT THERMOSTAT

  1. Remove the thermostat (Click here).

  1. Check the valve opening temperature of the thermostat.

    Standard:
    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.

  1. Reinstall the thermostat (Click here).



NG
REPLACE THERMOSTAT
OK

REPLACE HV CONTROL ECU