SFI SYSTEM, Diagnostic DTC:P0128

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

DESCRIPTION

At the same time as using the engine coolant temperature sensor to determine the engine coolant temperature, the ECM estimates the engine coolant temperature. If the difference between the estimated and actual engine coolant temperatures exceeds a predetermined value, then the DTC is stored, notifying of a malfunction in the functioning of the thermostat.

DTC No. DTC Detection Condition Trouble Area
P0128

Abnormal (open) thermostat functioning detected.

(2 trip detection logic)

  • Thermostat

  • Cooling system

  • Engine coolant temperature sensor

  • ECM

MONITOR DESCRIPTION

The ECM estimates the engine coolant temperature based on the starting temperature, engine loads, and engine speeds. The ECM then compares the estimated temperature with the actual engine coolant temperature. If the difference between the estimated engine coolant temperature and the actual engine coolant temperature exceeds the specified value, the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores the DTC.

CONFIRMATION DRIVING PATTERN

A004KP7E03

  1. Connect the GTS to the DLC3.

  2. Turn the ignition switch to ON and turn the GTS on.

  3. Clear DTCs (even if no DTCs are stored, perform the clear DTC operation) Click here.

  4. Turn the ignition switch off and wait for at least 30 seconds.

  5. Turn the ignition switch to ON and turn the GTS on.

  6. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

  7. Perform the following the confirmation driving pattern.

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.


    1. Drive the vehicle at 80 km/h (50 mph) or more for 20 minutes or more [A].

    2. Stop the vehicle.

    3. Idle the engine for 1 minute or more [B].

  8. Enter the following menus: Powertrain / Engine / Trouble Codes.

  9. Read pending DTCs.

    Tech Tips


    • If a pending DTC is output, the system is malfunctioning.

    • If a pending DTC is not output, perform the following procedure.

  10. Enter the following menus: Powertrain / Engine / Utility / All Readiness.

  11. Input the DTC: P0128.

  12. Check the DTC judgment result.

    GTS Display Description
    NORMAL

    • DTC judgment completed

    • System normal
    ABNORMAL

    • DTC judgment completed

    • System abnormal
    INCOMPLETE

    • DTC judgment not completed

    • Perform driving pattern after confirming DTC enabling conditions
    N/A

    • Unable to perform DTC judgment

    • Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

    Tech Tips


    • If the judgment result shows NORMAL, the system is normal.

    • If the judgment result shows ABNORMAL, the system has a malfunction.

  13. If the test result is INCOMPLETE or N/A and no DTC is output, perform a universal trip and check for permanent DTCs Click here.

    Tech Tips


    • If a permanent DTC is output, the system is malfunctioning.

    • If no permanent DTC is output, the system is normal.

CAUTION / NOTICE / HINT

Tech Tips


  • Read freeze frame data using the GTS. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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.

  • When the DTC is output, check the engine coolant temperature using the GTS. Enter the following menus: Powertrain / Engine / Data List / Coolant Temp. If the Coolant Temp value is lower than the actual engine coolant temperature, the engine coolant temperature sensor circuit may be malfunctioning. In this case, check the wire harnesses and connectors (and those connections) between the ECM and the engine coolant temperature sensor first.

PROCEDURE


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


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine / Trouble Codes.

    5. Read DTCs.

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

      Tech Tips

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


    B

    GO TO DTC CHART Click here

    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 cooling fan operation or any modifications.


    NG

    REPAIR OR REPLACE COOLING SYSTEM

    OK

  3. INSPECT THERMOSTAT


    1. Inspect the thermostat (thermostat opening temperature) Click here.


    OK

    REPLACE ECM Click here

    NG

    REPLACE THERMOSTAT Click here