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Home >> Infiniti >> 2004 >> QX56 AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System >> DTC P0420, P0430: Three Way Catalyst Function >> Diagnostic Procedure
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Diagnostic Procedure

  1. CHECK EXHAUST SYSTEM 

    Visually check exhaust tubes and muffler for dent.

    OK or NG

    OK: GO TO 2.

    NG: Repair or replace.

  2. CHECK EXHAUST GAS LEAK 
    1. Start engine and run it at idle.
    2. Listen for an exhaust gas leak before the three way catalyst (manifold).
      Fig 1: Checking Exhaust Gas Leak
      G02691408Courtesy of NISSAN MOTOR CO., U.S.A.

    OK or NG

    OK: GO TO 3.

    NG: Repair or replace.

  3. CHECK INTAKE AIR LEAK 

    Listen for an intake air leak after the mass air flow sensor.

    OK or NG

    OK: GO TO 4.

    NG: Repair or replace.

  4. CHECK IGNITION TIMING 

    Check the following items. Refer to BASIC INSPECTION .

    CHECK IGNITION TIMING

    Items Specifications
    Target idle speed 650+/-50rpm (in P or N position)
    Ignition timing 15+/-5°BTDC (in P or N position)

    OK or NG

    OK: GO TO 5.

    NG: Follow the BASIC INSPECTION .

  5. CHECK INJECTORS 
    1. Stop engine and then turn ignition switch ON.
    2. Check voltage between ECM terminals 21, 22, 23, 40, 41, 42, 44, 63 and ground with CONSULT-II or tester.

      Refer to Wiring Diagram for Injectors, WIRING DIAGRAM .

      Battery voltage should exist.

    OK or NG

    OK: GO TO 6.

    NG: Perform DIAGNOSTIC PROCEDURE .

    Fig 2: Checking Voltage Between ECM Terminals 21, 22, 23, 40, 41, 42, 44, 63 & Ground
    G02691409Courtesy of NISSAN MOTOR CO., U.S.A.
  6. CHECK IGNITION SPARK 
    1. Turn ignition switch OFF.
    2. Disconnect ignition coil assembly from rocker cover.
    3. Connect a known-good spark plug to the ignition coil assembly.
    4. Disconnect all injector harness connectors.
    5. Place end of spark plug against a suitable ground and crank engine.
    6. Check for spark.

    OK or NG

    OK: GO TO 7.

    NG: Check ignition coil with power transistor and their circuit.

    Refer to IGNITION SIGNAL .

    Fig 3: Checking Ignition Spark
    G02691410Courtesy of NISSAN MOTOR CO., U.S.A.
  7. CHECK INJECTOR 
    1. Turn ignition switch OFF.
    2. Remove injector assembly.

      Refer to FUEL INJECTOR AND FUEL TUBE .

      Keep fuel hose and all injectors connected to injector gallery.

    3. Disconnect all ignition coil harness connectors.
    4. Reconnect injector harness connector.
    5. Turn ignition switch ON.

      Make sure fuel does not drip from injector.

    OK or NG

    OK (Does not drip.): GO TO 8.

    NG (Drips.): Replace the injector(s) from which fuel is dripping.

  8. CHECK INTERMITTENT INCIDENT 

    Refer to TROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENT .

    Trouble is fixed.: INSPECTION END

    Trouble is not fixed.: Replace three way catalyst assembly.

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