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Home >> Infiniti >> 2023 >> QX55 Essential >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System (DTC/Circuit Diagnosis) (2 Of 5) >> DTC/Circuit Diagnosis >> DTC P0171: Fuel Injection System Function >> Diagnosis Procedure
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Diagnosis Procedure

  1. CHECK EXHAUST GAS LEAKAGE 
    1. Start engine and run it at idle.
    2. Listen for an exhaust gas leakage before three way catalyst (manifold).
      GNSDB6595Courtesy of NISSAN NORTH AMERICA, INC.

    Is exhaust gas leakage detected?

    YES

    Repair or replace malfunctioning part.

    NO

    GO TO 2.

  2. CHECK FOR INTAKE AIR LEAKAGE 
    1. Listen for an intake air leakage after the mass air flow sensor.
    2. Check PCV hose connection.

    Is intake air leakage detected?

    YES

    Repair or replace malfunctioning part.

    NO

    GO TO 3.

  3. CHECK A/F SENSOR 1 INPUT SIGNAL CIRCUIT 
    1. Turn ignition switch OFF.
    2. Disconnect corresponding A/F sensor 1 harness connector.
    3. Disconnect ECM harness connector.
    4. Check the continuity between A/F sensor 1 harness connector and ECM harness connector.

      A/F sensor 1

      ECM

      Continuity

      Connector

      Terminal

      Connector

      Terminal

      F18

      1

      F52

      86

      Existed

      2

      88
    5. Check the continuity between A/F sensor 1 harness connector and ground, or ECM harness connector and ground.

      A/F sensor 1

      --

      Continuity

      Connector

      Terminal

      F18

      1

      Ground

      Not existed

      2

      ECM

      --

      Continuity

      Connector

      Terminal

      F52

      86

      Ground

      Not existed

      88
    6. Also check harness for short to ground and short to power.

    Is the inspection result normal?

    YES

    GO TO 4.

    NO

    Repair or replace malfunctioning part.

  4. CHECK A/F SENSOR 1 FUNCTION-1 

    If DTC Confirmation Procedure has been previously conducted, always perform the following before conducting the next test.

    1. Turn ignition switch OFF and wait at least 10 seconds.
    2. Turn ignition switch ON.
    3. Turn ignition switch OFF and wait at least 10 seconds.

    TESTING CONDITION:

    Before performing the following procedure, confirm that battery voltage is more than 11 V at idle.

    GO TO 5.

  5. CHECK A/F SENSOR 1 FUNCTION CHECK-2 
    1. Clear the mixture ratio self-learning value. Refer to Description .
    2. Turn ignition switch OFF and wait at least 10 seconds.
    3. Turn ignition switch ON.
    4. Turn ignition switch OFF and wait at least 10 seconds.
    5. Start engine and keep the engine speed between 3, 500 and 4, 000 rpm for 1 minute under no load.
    6. Let engine idle for 1 minute.
    7. Keep engine speed between 2, 500 and 3, 000 rpm for 20 minutes.
    8. Check DTC.

    Is DTC detected?

    YES

    Replace A/F sensor. Refer to Removal and Installation .

    NO

    GO TO 6

  6. CHECK FUEL PRESSURE 

    Check fuel pressure. Refer to Work Procedure .

    Is the inspection result normal?

    YES

    GO TO 8.

    NO

    GO TO 7.

  7. DETECT MALFUNCTIONING PART 

    Check fuel hoses and fuel tubes for clogging.

    Is the inspection result normal?

    YES

    Replace "fuel filter and fuel pump assembly". Refer to Removal and Installation .

    NO

    Repair or replace malfunctioning part.

  8. CHECK MASS AIR FLOW SENSOR 

    SYMBOL With CONSULT

    1. Install all removed parts.
    2. Start the engine and warm it up to normal operating temperature.
    3. Check "MASS AIR FLOW SENSOR (Hz) B1" in "DATA MONITOR" mode of "ENGINE" using CONSULT.

      Monitor item

      Condition

      Indication

      MASS AIR FLOW SENSOR (Hz) B1

      Ignition switch ON (Engine stopped.)

      Approx. 3, 700 Hz

      Idle (Engine is warmed-up to normal operating temperature.)

      5, 000 - 5, 400 Hz

      2, 500 rpm (Engine is warmed-up to normal operating temperature.)

      5, 700 - 6, 300 Hz

      Idle to about 4, 000 rpm

      6, 300 - 7, 100 Hz*

      *: Check for linear frequency rise in response to increase of engine speed.

    SYMBOL Without CONSULT

    1. Install all removed parts.
    2. Start the engine and warm it up to normal operating temperature.
    3. Check the frequency between ECM harness connector terminals under the following conditions.

      ECM

      Condition

      Frequency

      Connector

      +

      -

      Terminal

      F51

      26

      23

      Ignition switch ON (Engine stopped.)

      Approx. 3, 700 Hz

      Idle (Engine is warmed-up to normal operating temperature.)

      5, 000 - 5, 400 Hz

      2, 500 rpm (Engine is warmed-up to normal operating temperature.)

      5, 700 - 6, 300 Hz

      Idle to about 4, 000 rpm

      6, 300 - 7, 100 Hz*

      *: Check for linear frequency rise in response to increase of engine speed.

    Is the inspection result normal?

    YES

    GO TO 9.

    NO

    Check connectors for rusted terminals or loose connections in the mass air flow sensor circuit or grounds. Refer to Diagnosis Procedure .

  9. CHECK FUNCTION OF DIRECT FUEL INJECTOR 

    SYMBOL With CONSULT

    1. Start the engine.
    2. Perform "POWER BALANCE" in "ACTIVE TEST" mode of "ENGINE" using CONSULT.
    3. Check that each circuit produces a momentary engine speed drop.

    SYMBOL Without CONSULT

    1. Start the engine and let it idle.
    2. Listen to each direct fuel injector operating sound.

      Clicking sound should be heard.
      GNSDB5851Courtesy of NISSAN NORTH AMERICA, INC.

    Is the inspection result normal?

    YES

    INSPECTION END

    NO

    Perform trouble diagnosis for direct fuel injector and circuit, refer to Diagnosis Procedure .

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