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SFI SYSTEM(w/ Canister Pump Module), Diagnostic DTC:P0128

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DTC Code DTC Name
P0128 Thermostat
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DESCRIPTION

This DTC is stored when the engine coolant temperature does not reach 75°C (167°F) despite sufficient engine warm-up time having elapsed.

DTC No. Detection Item DTC Detection Condition Trouble Area MIL Memory
P0128 Thermostat

All of the following conditions are met for 5 seconds (2 trip detection logic):

(a) Cold start

(b) The engine is warmed up

(c) The engine coolant temperature is less than 75°C (167°F)


  • Water inlet with thermostat sub-assembly

  • Cooling system

  • Engine coolant temperature sensor

  • ECM

Comes on DTC stored
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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. When the estimated engine coolant temperature reaches 75°C (167°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is less than 75°C (167°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores this DTC.

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MONITOR STRATEGY

Frequency of Operation Once per driving cycle
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CONFIRMATION DRIVING PATTERN


  1. Stop the engine and allow it to soak.

  2. Connect the GTS to the DLC3.

  3. Turn the engine switch on (IG) and turn the GTS on [A].

  4. Enter the following menus: Powertrain / Engine / Data List / All Data / Coolant Temp and Intake Air.

  5. Check that "Coolant Temp" is 56°C (133°F) or less and "Intake Air" is between 0 and 35°C (32 and 95°F).

  6. Set the heater to MAX HOT with fresh air mode selected and turn the A/C off.

  7. Start the engine and drive the vehicle at 80 km/h (50 mph) for 15 minutes [B].

    CAUTION:

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

    Tip:
    • Data can be captured relatively easily by using the snapshot function in the Data List.

    • Enter the following menus: Data List / Function / Snapshot Configure / Duration / 5 min.

    • Data capture can be started by using the target point function. For example, setting the target point to an engine speed of 4000 rpm and then racing the engine, etc. to raise the engine speed to a speed of 4000 rpm or higher will cause data capture to start.

  8. After "Coolant Temp" stabilizes, check that "Coolant Temp" is 75°C (167°F) or higher [C].

    Tip:

    If "Coolant Temp" is less than 75°C (167°F) while driving the vehicle at 80 km/h (50 mph), inspect the cooling system and thermostat.

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CAUTION / NOTICE / HINT

Tip:
  • When the DTC is output, check the engine coolant temperature using the GTS. Enter the following menus: Powertrain / Engine / Data List / All Data / 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.

  • 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.

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PROCEDURE


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


    1. Connect the GTS to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the GTS on.

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

    5. Read the DTCs.


      1. Powertrain > Engine > Trouble Codes


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

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


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    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.

      Result
      Proceed to
      OK
      NG

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    INSPECT WATER INLET WITH THERMOSTAT SUB-ASSEMBLY


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

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      Result
      Proceed to
      OK
      NG

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    INSPECT ENGINE COOLANT TEMPERATURE SENSOR


    1. Inspect the engine coolant temperature sensor.

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      Tip:

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

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      Result
      Proceed to
      OK
      NG