ECD SYSTEM (for DPF), Diagnostic DTC:P1251

DTC Code DTC Name
P1251 Turbocharger / Supercharger Overboost Condition (Too High)

DESCRIPTION

Tech Tips

Refer to DTC P0046 Click here.

P1251
DTC Detection Drive Pattern DTC Detection Condition Trouble Area
Vehicle being driven Boost pressure is higher than the threshold* for 5 seconds (1 trip detection logic).

  • Turbocharger sub-assembly

  • VN turbo link stuck malfunction

  • Extremely low battery voltage (P0560 stored simultaneously)

  • Intake system

  • Exhaust system

  • Electric EGR control valve assembly

  • EGR cooler

  • Injector assembly

  • Diesel throttle body assembly

  • ECM

Tech Tips

*: This value changes based on engine speed, atmospheric pressure and the engine coolant temperature (when the vehicle is being driven in 2nd gear with the accelerator pedal fully depressed and the engine speed at 3000 rpm, the value is between approximately 98 and 130 kPa).

Related Data List
DTC No. Data List
P1251

  • MAP

  • Target Booster Pressure

  • MAF

  • Target EGR Position

  • Actual EGR Valve Pos.

  • VN Turbo Command

  • Actual VN Position

  • Atmosphere Pressure

Tech Tips

If DTC P1251 is stored due to the VN turbo vane being stuck closed, the following symptoms may appear:


  • Vehicle surge when driving with full load

  • Sudden lack of power due to power being limited

WIRING DIAGRAM

Refer to DTC P0046 Click here.

INSPECTION PROCEDURE

Note


  • After replacing the ECM, the new ECM needs registration Click here and initialization Click here.

  • After replacing an injector assembly, the ECM needs registration Click here.

Tech Tips

Read freeze frame data using the intelligent tester. 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 FOR ANY OTHER DTCS OUTPUT (RECORD STORED DTC AND FREEZE FRAME DATA)


    1. Connect the intelligent tester to the DLC3.

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

    3. Enter the following menus: Powertrain / Engine and ECT / DTC.

    4. Read the DTCs.

      Tech Tips


      • Record the stored DTCs and freeze frame data.

      • Be sure to carefully examine "MAP" and "Target Booster Pressure" in the freeze frame data.

      Result
      Result Proceed to
      P1251 is output A
      P1251 and other DTCs are output B

      Tech Tips

      DC motor-related DTCs: P0046, P0047 and P0048 Click here.

      Nozzle vane position sensor-related DTCs: P2564 and P2565 Click here.


    B

    GO TO DTC CHART Click here

    A

  2. CHECK AIR INTAKE SYSTEM


    1. Check if the hoses between the air cleaner and turbocharger, and turbocharger and intake manifold are damaged or disconnected.

      Result
      Result Proceed to
      Hoses or pipes are damaged or disconnected A
      No hoses or pipes are damaged or disconnected B

      Tech Tips


      • Be sure to check if the hoses and pipes between the air cleaner and compressor are disconnected as disconnection of a hose or pipe can cause overboost. Also, check the high pressure hoses for disconnection due to overboost.

      • Check for disconnection of the exhaust pipes.

      • Using your hand, check whether the pipes and hoses in the intake system are securely connected.

      • Check for any modifications in the intake system made by the user.


    B

    CHECK TURBOCHARGER SUB-ASSEMBLY (DC MOTOR OPERATION) Click here

    A

  3. REPAIR OR REPLACE AIR INTAKE SYSTEM


    1. Repair or replace the malfunctioning part in the air intake system.


    NEXT

  4. CHECK TURBOCHARGER SUB-ASSEMBLY (DC MOTOR OPERATION)


    1. Check the turbocharger sub-assembly Click here.

      Tech Tips

      Check the movement of the actuator rod when the ignition switch is turned from ON to off.


    NG

    CHECK HARNESS AND CONNECTOR (ECM - TURBOCHARGER SUB-ASSEMBLY) Click here

    OK

  5. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (ACTIVATE THE EGR VALVE CLOSE)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine and warm it up, and make sure the A/C switch and all accessory switches are off.

    3. Turn the ignition switch off. Wait for 30 seconds, and then restart the engine.

    4. Turn the tester on.

    5. Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.

    6. Read the MAF value displayed on the tester while the engine is idling.

    7. Enter the following menus: Powertrain / Engine and ECT / Active Test / Activate the EGR Valve Close.

    8. Read the MAF value when the EGR valve is closed using the Active Test function.

      Tech Tips


      • If idling continues for 20 minutes or more, the EGR valve target opening angle becomes 0% (EGR valve fully closed). As this makes diagnosis impossible, it becomes necessary to drive the vehicle or to restart the engine.

      • Before performing the diagnosis, confirm that the EGR valve target opening angle is not 0%.

      • When "Coolant Temp" is 75°C (167°F) or higher during idling, the exhaust gas flows through the EGR cooler. If MAF does not change when the EGR is cut even though the EGR valve is operating normally, the EGR cooler may be clogged.

      • When idling while warming up the engine, the actuator operates and the EGR cooler is bypassed. However, if the connector of the VSV for the EGR cooler is disconnected, the EGR cooler is not bypassed and it is possible to check how clogged the EGR cooler is.

      Result
      Active Test Result Proceed to

      Activate the EGR Valve Close:

      Off (Open) to On (Closed)

      		 MAF value does not change A
      MAF value changes B

      Note

      As the measured values may differ from those shown below due to factors such as differences in measuring environments and changes in vehicle condition due to aging, do not use these values to determine whether the vehicle is malfunctioning or not.

      Tech Tips

      The problem may be a temporary one, due to the entry of deposits or foreign matter. Check that there are no deposits or foreign matter in the electric EGR control valve assembly or mass air flow meter.

      Reference
      EGR Valve Condition (Opening) Measuring Condition MAF (Reference)
      Open (67%)

      • Atmosphere pressure: 101 kPa

      • Intake air temperature: 30°C (86°F)

      • Engine coolant temperature: 88°C (190°F)

      		 3 to 12 gm/s
      Closed (0%) 7 gm/s or more

    B

    READ VALUE USING INTELLIGENT TESTER (INJECTION VOLUME) Click here

    A

  6. READ VALUE USING INTELLIGENT TESTER (TARGET EGR POSITION AND ACTUAL EGR VALVE POS.)


    1. Check the change in the values of "Target EGR Position" and "Actual EGR Valve Pos." in the Data List from the time when the "Control the EGR Step Position" or "Activate the EGR valve Close" Active Test was performed in the previous step.

      Result
      Result Proceed to
      Even though "Target EGR Position" indicated that the system was commanding the valve to open, "Actual EGR Valve Pos." remained near 0% and did not change A
      Other than above ("Actual EGR Valve Pos." changed according to the EGR valve open/close commands of the Active Test) B

    B

    REPLACE EGR COOLER Click here

    A

  7. REMOVE DEPOSIT (ELECTRIC EGR CONTROL VALVE ASSEMBLY)


    1. Remove the electric EGR control valve assembly Click here.

    2. Visually check the electric EGR control valve assembly for deposits. If there are deposits, clean the electric EGR control valve assembly.

      Note


      • When cleaning the electric EGR control valve assembly, make sure the valve is completely closed.

      • When cleaning the electric EGR control valve assembly, perform initialization procedure Click here.

      • Do not forcibly open the valve, as it may be damaged or deformed.

      • When cleaning the electric EGR control valve assembly, use a piece of cloth soaked with cleaning solvent. Spraying the solvent directly onto these parts or soaking the parts in the solvent may damage the parts.

      Tech Tips


      • If the EGR valve is stuck closed, the intake air amount increases and engine vibration may worsen.

      • If the EGR valve does not close properly or is stuck open, EGR becomes excessive and combustion becomes unstable. Also, there may be a lack of power.

    3. Reinstall the electric EGR control valve assembly Click here.


    NEXT

    CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED Click here

  8. REPLACE EGR COOLER


    1. Replace the EGR cooler Click here.


    NEXT

    CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED Click here

  9. READ VALUE USING INTELLIGENT TESTER (INJECTION VOLUME)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine and warm it up until the engine coolant temperature reaches 70°C (158°F) or higher.

    3. Allow the engine to idle for 1 minute or more.

      Tech Tips

      The A/C switch and all accessory switches should be off with a fully warm engine.

    4. Turn the tester on.

    5. Enter the following menus: Powertrain / Engine and ECT / Data List / Injection Volume.

    6. Read the values during engine idling.

      Result
      Result Proceed to

      Injection Volume is less than 5 mm3/st

      		 A
      Except above B

      Tech Tips


      • If the injector assembly is malfunctioning, the compensatory injection volume remains at 5.0 mm3/st.

      • If there is a disconnection, the feedback value will increase and +5.0 mm3/st will be indicated, because it will become impossible for the injector to inject.


    B

    CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED Click here

    A

  10. REPLACE INJECTOR ASSEMBLIES OF ALL CYLINDERS


    1. Replace the injector assemblies Click here.

      Note


      • When replacing the injector assembly for a cylinder, always be sure to use a new injection pipe.

      • Follow the procedure in the repair manual and temporarily install the injection pipes and nozzle leakage pipe, and then correctly position the injector assemblies. After that, tighten parts according to the torque specifications.

      • If the installation procedure is not performed correctly, injector assemblies may become out of position, which may cause the injector assemblies to deteriorate, resulting in malfunctions.

      • If an injector assembly deteriorates and malfunctions, other problems such as knocking, rough idle, etc. may occur.

      • If an injector assembly becomes out of position, it is possible that the seal between the injector assembly and injection pipe may become incomplete, resulting in a fuel leak.


    NEXT

  11. BLEED AIR FROM FUEL SYSTEM


    1. Bleed the air from the fuel system Click here.


    NEXT

  12. REGISTER INJECTOR COMPENSATION CODE AND PERFORM PILOT QUANTITY LEARNING


    1. Register the injector compensation code Click here.

    2. Perform the injector pilot quantity learning Click here.


    NEXT

  13. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED


    1. Connect the intelligent tester to the DLC3.

    2. Clear the DTCs Click here.

    3. Turn the ignition switch off.

    4. Start the engine and warm it up.

    5. Confirm the value of Engine Speed from the Freeze Frame Data recorded previously, and then drive the vehicle according to the Engine Speed value.

      Tech Tips

      Take a snapshot of "MAP" and "Target Boost Pressure" in the Data List with the intelligent tester while driving the vehicle.

    6. Read the DTCs.

      Result
      Result Proceed to
      P1251 is not output and the amount by which MAP exceeds Target Boost Pressure is 20 kPa or less A
      Except above B*

      Tech Tips

      *: Return to "Check Air Intake System" and inspect areas that have not been inspected yet.


    B

    CHECK AIR INTAKE SYSTEM Click here

    A

    END

  14. CHECK HARNESS AND CONNECTOR (ECM - TURBOCHARGER SUB-ASSEMBLY)


    1. Disconnect the DC motor connector.

    2. Disconnect the nozzle vane position sensor connector.

    3. Disconnect the ECM connector.

    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance
      Tester Connection Condition Specified Condition
      S1-2 (M-) - B39-107 (M-) Always Below 1 Ω
      S1-1 (M+) - B39-108 (M+) Always Below 1 Ω
      S2-3 (VTA) - B39-124 (VNA) Always Below 1 Ω
      S2-2 (E2) - B39-100 (VNE2) Always Below 1 Ω
      S2-1 (VC) - B39-101 (VNVC) Always Below 1 Ω
      S1-2 (M-) or B39-107 (M-) - Body ground Always 10 kΩ or higher
      S1-1 (M+) or B39-108 (M+) - Body ground Always 10 kΩ or higher
      S2-3 (VTA) or B39-124 (VNA) - Body ground Always 10 kΩ or higher
      S2-1 (VC) or B39-101 (VNVC) - Body ground Always 10 kΩ or higher

    5. Reconnect the DC motor connector.

    6. Reconnect the nozzle vane position sensor connector.

    7. Reconnect the ECM connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

    INSPECT TURBOCHARGER SUB-ASSEMBLY Click here