ECD SYSTEM, Diagnostic DTC:P1251

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

DESCRIPTION

Refer to DTC P0046.

Click here

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

MIL

Memory

P1251

Turbocharger / Supercharger Overboost Condition (Too High)

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 pipe with cooler sub-assembly

  • Injector assembly

  • Diesel throttle body assembly

  • ECM

Comes on

DTC stored
Tip:

*: 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).

Table 1. 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
Tip:

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

CONFIRMATION DRIVING PATTERN

DTC No.

DTC Detection Drive Pattern

P1251

Vehicle being driven

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 (Click here) and initialization (Click here).

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

    Click here

Tip:

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: Powertrain / Engine and ECT / Trouble Codes.

    4. Read the DTCs.

      Powertrain > Engine > Trouble Codes

      Tip:

      • 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

      DTC P1251 is output

      A

      DTC P1251 and other DTCs are output

      B
      Tip:

      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 hereClick here

    A

  2. CHECK INTAKE SYSTEM

    1. Check if the hoses between the air cleaner case sub-assembly and turbocharger sub-assembly, and turbocharger sub-assembly 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
      Tip:

      • 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 INTAKE SYSTEM

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

    Result

    Proceed to

    NEXT
    NEXT

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

    1. Check the turbocharger sub-assembly.

      Click here

      Tip:

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

    Result

    Proceed to

    OK

    NG
    NG

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

    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 and wait for 30 seconds.

    4. Start the engine and turn the GTS on.

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

      Powertrain > Engine > Data List

      Tester Display

      MAF

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

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

      Powertrain > Engine > Active Test

      Active Test Display

      Activate the EGR Valve Close

      Data List Display

      MAF

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

      Tip:

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

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

      • When idling while warming up the engine, the actuator operates and the EGR pipe with cooler sub-assembly is bypassed. However, if the connector of the No. 1 vacuum switching valve assembly (for EGR cooler) is disconnected, the EGR pipe with cooler sub-assembly is not bypassed and it is possible to check if the EGR pipe with cooler sub-assembly is clogged.

      Result

      GTS Display

      Result

      Proceed to

      Activate the EGR Valve Close:

      OFF (Open) to Close

      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.

      Tip:

      The problem may be a temporary, 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 assembly.

      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/sec

      Closed (0%)

      7 gm/sec or more
    B

    READ VALUE USING GTS (INJECTION VOLUME)Click here

    A

  6. READ VALUE USING GTS (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 "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 PIPE WITH COOLER SUB-ASSEMBLYClick here

    A

  7. CHECK FOR 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 solvent directly onto these parts or soaking the parts in solvent may damage the parts.

      • When cleaning the EGR control valve, care should be taken to prevent the ingress of cleaning solvent into the bearings of valve shaft, and when wiping off deposits on the EGR control valve, care should be taken not to push the deposits into the bearings of valve shaft. These contaminants may adversely affect on the function of EGR control valve.

      Tip:

      • 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, the amount of recirculated exhaust gas becomes excessive and combustion becomes unstable. Also, there may be a lack of power.

    Result

    Proceed to

    NEXT
    NEXT

    CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIREDClick here

  8. REPLACE EGR PIPE WITH COOLER SUB-ASSEMBLY

    1. Replace the EGR pipe with cooler sub-assembly.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

    CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIREDClick here

  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.

      Tip:

      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: Powertrain / Engine and ECT / Data List / All Data / Injection Volume.

      Powertrain > Engine > Data List

      Tester Display

      Injection Volume

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

      Result

      Result

      Proceed to

      Injection Volume is less than 5 mm3/st

      A

      Except above

      B
      Tip:

      • 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 REPAIREDClick 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.

    Result

    Proceed to

    NEXT
    NEXT

  11. BLEED AIR FROM FUEL SYSTEM

    1. Bleed the air from the fuel system.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

  12. REGISTER INJECTOR COMPENSATION CODE AND PERFORM PILOT QUANTITY LEARNING

    1. Register the injector compensation codes.

      Click here

    2. Perform the pilot quantity learning.

      Click here

    Result

    Proceed to

    NEXT
    NEXT

  13. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs.

      Powertrain > Engine > Clear DTCs

    5. Turn the ignition switch off and wait for 30 seconds.

    6. Start the engine and warm it up.

    7. Turn the GTS on.

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

      CAUTION:

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

      Tip:

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

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

    10. Read the DTCs.

      Powertrain > Engine > Trouble Codes

      Result

      Result

      Proceed to

      DTC P1251 is not output and the amount by which MAP exceeds Target Boost Pressure is 20 kPa or less

      A

      Except above*

      B
      Tip:

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

    A

    END

    B

    CHECK INTAKE SYSTEMClick here

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

    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

      j1-2 (MA) - B76-107 (M-)

      Always

      Below 1 Ω

      j1-1 (MB) - B76-108 (M+)

      Always

      Below 1 Ω

      j2-3 (VTA) - B76-124 (VNA)

      Always

      Below 1 Ω

      j2-2 (E2) - B76-100 (VNE2)

      Always

      Below 1 Ω

      j2-1 (VC) - B76-101 (VNVC)

      Always

      Below 1 Ω

      j1-2 (MA) or B76-107 (M-) - Body ground

      Always

      10 kΩ or higher

      j1-1 (MB) or B76-108 (M+) - Body ground

      Always

      10 kΩ or higher

      j2-3 (VTA) or B76-124 (VNA) - Body ground

      Always

      10 kΩ or higher

      j2-1 (VC) or B76-101 (VNVC) - Body ground

      Always

      10 kΩ or higher

    Result

    Proceed to

    OK

    NG
    OK

    INSPECT TURBOCHARGER SUB-ASSEMBLY

    Click here

    NG

    REPLACE HARNESS OR CONNECTOR