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Home >> Nissan-Datsun >> 2004 >> Altima Base, Automatic >> Repair and Diagnosis >> Engine Performance >> Engine Control System - 2.5L >> DTC P0420: 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

    1. OK : GO TO 2.
    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 Three Way Catalyst For Exhaust Gas Leak
      G02884435Courtesy of NISSAN MOTOR CO., U.S.A.

    OK or NG

    1. OK : GO TO 3.
    2. NG : Repair or replace.
  3. CHECK INTAKE AIR LEAK 

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

    OK or NG

    1. OK : GO TO 4.
    2. NG : Repair or replace.
  4. CHECK IGNITION TIMING 

    Check for ignition timing. Refer to "BASIC INSPECTION ".

    TARGET IDLE SPEED AND IGNITION TIMING SPECIFICATIONS

    Items Specifications
    Target idle speed A/T 700 +/- 50 RPM (in P or N position)
    Target idle speed M/T 700 +/- 50 RPM
    Ignition timing A/T 15 +/- 5° BTDC (in P or N position)
    Ignition timing M/T 15 +/- 5° BTDC

    OK or NG

    1. OK : GO TO 5.
    2. NG : Follow the Basic Inspection.
  5. CHECK INJECTORS 
    1. Refer to Wiring Diagram for Injectors, see WIRING DIAGRAM  .
    2. Stop engine and then turn ignition switch ON.
    3. Check voltage between ECM terminals 22, 23, 41, 42 and ground with CONSULT-II or tester.

      Battery voltage should exist. 

    OK or NG

    1. OK : GO TO 6.
    2. NG : Perform DIAGNOSTIC PROCEDURE .
      Fig 2: Checking Voltage Between ECM Terminals 22, 23, 41, 42 & Ground
      G02884436Courtesy 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. Place end of spark plug against a suitable ground and crank engine.
    5. Check for spark.

    OK or NG

    1. OK : GO TO 7.
    2. NG : Check ignition coil with power transistor and their circuit.
      Fig 3: Checking Ignition Spark
      G02884437Courtesy 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 ignition coil assembly harness connector.
    4. Turn ignition switch ON.

      Make sure fuel does not drip from injector.

    OK or NG

    1. OK (Does not drip) : GO TO 8.
    2. NG (Drips) : Replace the injector(s) from which fuel is dripping.
  8. CHECK INTERMITTENT INCIDENT 

    Preform "TROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENT ".

    1. Trouble is fixed : INSPECTION END 
    2. Trouble is not fixed : Replace three way catalyst (manifold).
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