ECD SYSTEM, Diagnostic DTC:P0401

DTC Code DTC Name
P0401 Exhaust Gas Recirculation "A" Flow Insufficient Detected

DESCRIPTION

The exhaust gas recirculation is a measure to reduce the formation of nitrogen oxides (NOx). Nitrogen oxides are produced in large quantities when combustion occurs with excess air and at a very high temperature. The oxygen and nitrogen of the combustion air combine to form nitric oxide (NO) and nitrogen dioxide (NO2). The EGR is the diesel engine isolated at idle and always needed in the partial load range, because it is working with a very large excess of air.

Mixing the recirculated exhaust gas with fresh air renders it inert, decreasing the amount of oxygen and nitrogen inside the cylinder and lowering the combustion temperature to a maximum of 500°C (932°F).

The recirculated exhaust gas is cooled by the EGR cooler to further increase this effect.

The amount of averaging used for more accurate adaptation of the exhaust gas recirculation to tolerances of the injection amounts.

An average overall cylinder injection quantity is determined from the measured value by the air fuel ratio sensor and that measured by the mass air flow meter sub-assembly. This value is compared to the injection quantity predetermined by the ECM. If a deviation is detected, the air mass is corrected by adjusting the EGR actuator to the actual injection quantity to set the correct air fuel ratio value. The amount of average adaptation is not a quick scheme but an adaptive learning process. This means that the injection quantity error is taught in an adaptive map which is stored in the ECM permanently.

Tech Tips

For more information on the EGR control, refer to System Description.

Click here

DTC No. Detection Item DTC Detection Condition Trouble Area MIL Memory
P0401 Exhaust Gas Recirculation "A" Flow Insufficient Detected

During normal operation, EGR negative deviation falls below limit value, or EGR rate exceeds limit value for 7.5 seconds.

(3 trip detection logic)

  • Intake system air leak

  • Exhaust system exhaust gas leak

  • Diesel throttle body assembly

  • EGR valve assembly

  • Turbocharger sub-assembly

  • EGR cooler assembly

  • ECM

 Comes on DTC stored

CAUTION / NOTICE / HINT

Note


  • When replacing the ECM, the ECM needs registration and initialization.

    Click here

  • After replacing the EGR valve assembly, the ECM needs initialization.

    Click here

  • After replacing the mass air flow meter sub-assembly, the ECM needs initialization.

    Click here

Tech Tips


  • When the ECM must be replaced, before replacing the ECM, perform the "Learning Values Save" function using the GTS. Then after installing the new ECM, perform all of the initialization/registrations for the "Learning Values Write" function by following the instructions shown on the GTS display.

  • Read freeze frame data using the GTS. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, and other data from the time the malfunction occurred.

PROCEDURE


  1. CHECK INTAKE SYSTEM


    1. Check for air leaks in the intake system after the turbocharger sub-assembly.

      OK
      No leakage.
      Result
      Proceed to
      OK
      NG

    NG

    REPAIR OR REPLACE INTAKE SYSTEM Click here

    OK

  2. CHECK MASS AIR FLOW METER SUB-ASSEMBLY


    1. Check for DTCs related to the validity of the mass air flow meter sub-assembly.

      Result
      Proceed to
      OK
      NG

    OK

    GO TO STEP 4 Click here

    NG

  3. CHECK EXHAUST SYSTEM


    1. Check for exhaust gas leaks in the exhaust system before the turbocharger sub-assembly.

      OK
      No leakage.
      Result
      Proceed to
      OK
      NG

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM Click here

    OK

  4. CHECK DIESEL THROTTLE BODY ASSEMBLY


    1. Check for DTCs related to the diesel throttle body assembly.

      OK
      DTCs related to the diesel throttle body assembly are not output.
      Result
      Proceed to
      OK
      NG

    NG

    REPAIR OR REPLACE DIESEL THROTTLE BODY ASSEMBLY Click here

    OK

  5. CHECK EGR VALVE ASSEMBLY


    1. Check for DTCs related to the EGR valve assembly.

      OK
      DTCs related to the EGR valve assembly are not output.
      Result
      Proceed to
      OK
      NG

    NG

    REPAIR OR REPLACE EGR VALVE ASSEMBLY Click here

    OK

  6. CHECK TURBOCHARGER SUB-ASSEMBLY


    1. Check for DTCs related to the turbocharger sub-assembly.

      OK
      DTCs related to the turbocharger sub-assembly are not output.
      Result
      Proceed to
      OK
      NG

    NG

    REPAIR OR REPLACE TURBOCHARGER SUB-ASSEMBLY Click here

    OK

  7. CHECK EGR COOLER ASSEMBLY


    1. Check that the airflow is not slowed by soot deposits in the EGR cooler.

      OK
      Airflow is not slowed by soot deposits.
      Result
      Proceed to
      OK
      NG

    NG

    CLEAN OR REPLACE EGR COOLER ASSEMBLY Click here

    OK

  8. CHECK WHETHER DTC OUTPUT RECURS (DTC P0401)


    1. Connect the GTS to the DLC3.

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

    3. Clear the DTCs.


      Powertrain > Engine and ECT > Clear DTCs

    4. Turn the ignition switch off and wait for 60 seconds or more [A].

    5. Perform road test [B].

    6. Repeat [A] and [B] for the number of trips detected.

    7. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.


      Powertrain > Engine and ECT > Trouble Codes

    8. Read the DTCs.

      Result
      Result Proceed to
      No DTC output A
      DTC P0401 B

    A

    END

    B

  9. REPLACE ECM


    1. Replace the ECM.

      Click here

      Result
      Proceed to
      NEXT

    NEXT

    GO TO STEP 16 Click here

  10. CLEAN OR REPLACE EGR COOLER ASSEMBLY


    1. Clean or replace the EGR cooler assembly.

      Result
      Proceed to
      NEXT

    NEXT

    GO TO STEP 16 Click here

  11. REPAIR OR REPLACE TURBOCHARGER SUB-ASSEMBLY


    1. Repair or replace turbocharger sub-assembly or perform inspections and troubleshooting for related DTCs.

      Click here

      Result
      Proceed to
      NEXT

    NEXT

    GO TO STEP 16 Click here

  12. REPAIR OR REPLACE EGR VALVE ASSEMBLY


    1. Repair or replace EGR valve assembly or perform inspections and troubleshooting for related DTCs.

      Click here

      Tech Tips

      When the EGR valve assembly is replaced, perform initialization.

      Click here

      Result
      Proceed to
      NEXT

    NEXT

    GO TO STEP 16 Click here

  13. REPAIR OR REPLACE DIESEL THROTTLE BODY ASSEMBLY


    1. Repair or replace diesel throttle body assembly or perform inspections and troubleshooting for related DTCs.

      Click here

      Result
      Proceed to
      NEXT

    NEXT

    GO TO STEP 16 Click here

  14. REPAIR OR REPLACE EXHAUST SYSTEM


    1. Repair or replace the malfunctioning parts of the exhaust system.

      Result
      Proceed to
      NEXT

    NEXT

    GO TO STEP 16 Click here

  15. REPAIR OR REPLACE INTAKE SYSTEM


    1. Repair or replace the malfunctioning parts of the intake system.

      Result
      Proceed to
      NEXT

    NEXT

  16. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED


    1. Connect the GTS to the DLC3.

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

    3. Clear the DTCs.


      Powertrain > Engine and ECT > Clear DTCs

    4. Turn the ignition switch off and wait for 60 seconds or more [A].

    5. Perform road test [B].

    6. Repeat [A] and [B] for the number of trips detected.

    7. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.


      Powertrain > Engine and ECT > Trouble Codes

    8. Confirm that the DTC is not output again.

      Result
      Proceed to
      NEXT

    NEXT

    END