ECD SYSTEM(w/ 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 2 seconds (1 trip detection logic).
  • Turbocharger sub-assembly

  • VN turbo link stuck malfunction

  • Extremely low battery voltage (P0560 stored simultaneously)

  • Intake system

  • Exhaust system

  • EGR valve assembly

  • EGR cooler

  • EGR system line deposits or clogs

  • Injector assembly

  • Diesel throttle body assembly

  • ECM

  • DPF catalytic converter or CCo catalytic converter cracks or removal

Tech Tips

*: This value changes based on engine speed, atmospheric pressure, intake air temperature and the engine coolant temperature.


Related Data List
DTC No. Data List
P1251
  • MAP

  • Target Booster Pressure

  • MAF

  • Target EGR Valve Pos

  • Target EGR Valve Pos #2

  • Actual EGR Valve Pos

  • Actual EGR Valve Pos #2

  • Actual VN Turbo Position

  • Actual VN Turbo Position #2

  • 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.

Refer to DTC P2564 Click here.

CAUTION / NOTICE / HINT

Note


  • After replacing the ECM, the new ECM needs registration (See page ) and initialization Click here.

  • After replacing the fuel supply pump assembly, the ECM needs initialization Click here.

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

Tech Tips

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 FOR ANY OTHER DTCS OUTPUT (RECORD STORED DTC AND FREEZE FRAME DATA)


    1. Connect the GTS to the DLC3.

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

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

    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 Click here:


        • P0046, P0047 and P0048 (for bank 1).

        • P004B, P004C and P004D (for bank 2).

      • Nozzle vane position sensor-related DTCs Click here:


        • P2564 and P2565 (for bank 1).

        • P2588 and P2589 (for bank 2).


    B
    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
    A
  3. REPAIR OR REPLACE AIR INTAKE SYSTEM


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


    NEXT
  4. PERFORM ACTIVE TEST USING GTS (OPERATE TURBOCHARGERSUB-ASSEMBLY)


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Engine and ECT / Active Test / Test the Turbo Charger Step Motor (Test the Turbo Charger Step Motor #2) / Data List / Target VN Turbo Position (Target VN Turbo Position #2) and Actual VN Turbo Position (Actual VN Turbo Position #2).

    5. While changing the Active Test value to 20, 95, 60 and 20%, check that Actual VN Turbo Position (Actual VN Turbo Position #2) smoothly changes to the set opening amount.

      Note

      When moving the vanes toward the fully closed position, make sure that Actual VN Turbo Position (Actual VN Turbo Position #2) does not become 5% or less.

      OK
      The Actual VN Turbo Position (Actual VN Turbo Position #2) value follows the Target VN Turbo Position (Target VN Turbo Position #2).

    NG
    OK
  5. PERFORM ACTIVE TEST USING GTS (ACTIVATE THE EGR VALVE CLOSE)


    1. Connect the GTS 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 GTS on.

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

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

    7. Enter the following menus: 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 lift amount 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 lift amount 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.

      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 EGR valve assembly or mass air flow meter.

      Reference
      EGR Valve Condition (Opening) Measuring Condition MAF (Reference)
      Open (40%)
      • Atmosphere pressure: 101 kPa

      • Engine coolant temperature: 75°C (167°F)

      3 to 10 gm/sec
      Closed (0%) 14 to 23 gm/sec

    B
    A
  6. READ VALUE USING GTS (TARGET EGR POS AND ACTUAL EGR VALVE POS)


    1. Check the change in the values of "Target EGR Valve Pos (Target EGR Valve Pos #2)" and "Actual EGR Valve Pos (Actual EGR Valve Pos #2)" in the Data List from the time when the "Control the EGR Step Position (Control the EGR Step Position #2)" or "Activate the EGR valve Close" Active Test was performed in the previous step.

      Result
      Result Proceed to
      Even though "Target EGR Valve Pos (Target EGR Valve Pos #2)" indicated that the system was commanding the valve to open, "Actual EGR Valve Pos (Actual EGR Valve Pos #2)" remained near 0% and did not change A
      Other than above ("Actual EGR Valve Pos (Actual EGR Valve Pos #2)" changed according to the EGR valve open/close commands of the Active Test) B

    B
    A
  7. REMOVE DEPOSIT (EGR VALVE ASSEMBLY)


    1. Remove the No. 1 and No. 2 EGR valve assembly Click here.

    2. Visually check the No. 1 and No. 2 EGR valve assembly for deposits. If there are deposits, clean the No. 1 and No. 2 EGR valve assembly.

      Note


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

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

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

      • When cleaning the EGR 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 EGR valve assembly Click here.


    NEXT
  8. REPLACE EGR COOLER


    1. Replace the EGR cooler Click here.


    NEXT
  9. READ VALUE USING GTS (INJECTION VOLUME)


    1. Connect the GTS 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 GTS on.

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

    6. Check the value of Injection Volume at 4000 rpm without load.

      Result
      Result Proceed to

      Injection Volume is less than 9 mm3/st

      A
      Except above B

    B
    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.

    2. Perform PM forced regeneration Click here.

      Tech Tips

      When fuel lines are disconnected, air may enter the fuel lines, leading to engine starting trouble. Therefore, perform forced regeneration and bleed the air from the fuel lines.


    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 GTS 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 GTS 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.


    A
    B
  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
      for LHD
      Tester Connection Condition Specified Condition
      C90-2 (M+) - C45-86 (M+) Always Below 1 Ω
      C90-1 (M-) - C45-85 (M-) Always Below 1 Ω
      C89-3 (VNVC) - C45-120 (VNVC) Always Below 1 Ω
      C89-2 (VNE2) - C45-97 (VNE2) Always Below 1 Ω
      C89-1 (VTA1) - C45-74 (VNA) Always Below 1 Ω
      z67-2 (M2+) - C45-18 (VN2+) Always Below 1 Ω
      z67-1 (M2-) - C45-41 (VN2-) Always Below 1 Ω
      z66-3 (VNC2) - C45-120 (VNVC) Always Below 1 Ω
      z66-2 (VE2) - C45-97 (VNE2) Always Below 1 Ω
      z66-1 (VTI2) - C45-117 (VNA2) Always Below 1 Ω
      C90-2 (M+) or C45-86 (M+) - Body ground Always 10 kΩ or higher
      C90-1 (M-) or C45-85 (M-) - Body ground Always 10 kΩ or higher
      C89-3 (VNVC) or C45-120 (VNVC) - Body ground Always 10 kΩ or higher
      C89-1 (VTA1) or C45-74 (VNA) - Body ground Always 10 kΩ or higher
      z67-2 (M2+) or C45-18 (VN2+) - Body ground Always 10 kΩ or higher
      z67-1 (M2-) or C45-41 (VN2-) - Body ground Always 10 kΩ or higher
      z66-3 (VNC2) or C45-120 (VNVC) - Body ground Always 10 kΩ or higher
      z66-1 (VTI2) or C45-117 (VNA2) - Body ground Always 10 kΩ or higher
      for RHD
      Tester Connection Condition Specified Condition
      C90-2 (M+) - C46-86 (M+) Always Below 1 Ω
      C90-1 (M-) - C46-85 (M-) Always Below 1 Ω
      C89-3 (VNVC) - C46-120 (VNVC) Always Below 1 Ω
      C89-2 (VNE2) - C46-97 (VNE2) Always Below 1 Ω
      C89-1 (VTA1) - C46-74 (VNA) Always Below 1 Ω
      z67-2 (M2+) - C46-18 (VN2+) Always Below 1 Ω
      z67-1 (M2-) - C46-41 (VN2-) Always Below 1 Ω
      z66-3 (VNC2) - C46-120 (VNVC) Always Below 1 Ω
      z66-2 (VE2) - C46-97 (VNE2) Always Below 1 Ω
      z66-1 (VTI2) - C46-117 (VNA2) Always Below 1 Ω
      C90-2 (M+) or C46-86 (M+) - Body ground Always 10 kΩ or higher
      C90-1 (M-) or C46-85 (M-) - Body ground Always 10 kΩ or higher
      C89-3 (VNVC) or C46-120 (VNVC) - Body ground Always 10 kΩ or higher
      C89-1 (VTA1) or C46-74 (VNA) - Body ground Always 10 kΩ or higher
      z67-2 (M2+) or C46-18 (VN2+) - Body ground Always 10 kΩ or higher
      z67-1 (M2-) or C46-41 (VN2-) - Body ground Always 10 kΩ or higher
      z66-3 (VNC2) or C46-120 (VNVC) - Body ground Always 10 kΩ or higher
      z66-1 (VTI2) or C46-117 (VNA2) - 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.


    OK
    NG