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Home >> Nissan-Datsun >> 2006 >> Sentra Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - DTCS P0137 To P0445 (QG18DE) >> DTC P0420 Three Way Catalyst Function >> Diagnostic Procedure

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: Inspecting For Exhaust Gas Leaks
      G04191081Courtesy 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 for ignition timing. Refer to "BASIC INSPECTION ".

    IGNITION TIMING REFERENCE

    Items Specifications
    Target idle speed A/T 800 +/- 50 rpm (in P or N position)
    M/T 650 +/- 50 rpm
    Ignition timing A/T 18 +/- 5°BTDC (in P or N position)
    M/T 7 +/- 5°BTDC

    OK or NG 

    OK: GO TO  5.

    NG: Follow the "BASIC INSPECTION ".

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

      Refer to "WIRING DIAGRAM ".

      : Battery voltage should exist  .

      3. Fig 2: Checking Voltage Between ECM Terminals 22, 23, 41, 42 And Ground
      G04191161Courtesy of NISSAN MOTOR CO., U.S.A.

    OK or NG 

    OK: GO TO  6.

    NG: Perform Diagnostic Procedure FUEL INJECTOR. See "FUEL INJECTOR "

  6. CHECK FUNCTION OF IGNITION COIL-I 
    CAUTION: Do the following procedure in the place where ventilation is good without the combustibles.
    1. Turn ignition switch OFF.
    2. Remove fuel pump fuse in fuse and fusible link box to release fuel pressure.
      NOTE: Do not use CONSULT-II to release fuel pressure, or fuel pressure applies again during the following procedure.
      3. Fig 3: Removing Fuel Pump Fuse In Fuse And Fusible Link Box
      G04191162Courtesy of NISSAN MOTOR CO., U.S.A.
    3. Start engine.
    4. After engine stalls, crank it two or three times to release all fuel pressure.
    5. Turn ignition switch OFF.
    6. Remove all ignition coil harness connectors to avoid the electrical discharge from the ignition coils.
    7. Remove ignition coil and spark plug of the cylinder to be checked.
    8. Crank engine for five seconds or more to remove combustion gas in the cylinder.
    9. Connect spark plug and harness connector to ignition coil.
    10. Fix ignition coil using a rope etc. with gap of 13 - 17 mm between the edge of the spark plug and grounded metal portion as shown in the figure.
    11. Crank engine for about three seconds, and check whether spark is generated between the spark plug and the grounded metal portion.

      Spark should be generated  .

      12. Fig 4: Checking For Spark Between Spark Plug And Grounded Metal On Engine
      G04074892Courtesy of NISSAN MOTOR CO., U.S.A.
    CAUTION:
    • Do not approach to the spark plug and the ignition coil within 50cm. Be careful not to get an electrical shock while checking, because the electrical discharge voltage becomes 20kV or more.
    • It might cause to damage the ignition coil if the gap of more than 17 mm is taken.
    NOTE: When the gap is less than 13 mm, the spark might be generated even if the coil is malfunctioning.

    OK or NG 

    OK: GO TO  9.

    NG: GO TO  7.

  7. CHECK FUNCTION OF IGNITION COIL-II 
    1. Turn ignition switch OFF.
    2. Disconnect spark plug and connect a known-good spark plug.
    3. Crank engine for about three seconds, and recheck whether spark is generated between the spark plug and the grounded metal portion.

      Spark should be generated  .

    OK or NG 

    OK: GO TO  8.

    NG: Check ignition coil, power transistor and their circuits. Refer to IGNITION SIGNAL .

  8. CHECK FUNCTION OF IGNITION COIL-III 
    1. Reconnect the initial spark plugs.
    2. Crank engine for about three seconds, and recheck whether spark is generated between the spark plug and the grounded portion.

      Spark should be generated  .

    OK or NG 

    OK: INSPECTION END 

    NG: Replace spark plug(s) with standard type one(s). For spark plug type, refer to CHANGING SPARK PLUGS (DOUBLE PLATINUM - TIPPED TYPE) .

  9. CHECK FUEL INJECTOR 
    1. Turn ignition switch OFF.
    2. Remove fuel tube assembly. Refer to "FUEL INJECTOR AND FUEL TUBE ".

      Keep fuel hose and all fuel injectors connected to fuel tube.

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

      Make sure fuel does not drip from fuel injector.

    OK or NG 

    OK (Does not drip): GO TO  10.

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

  10. CHECK INTERMITTENT INCIDENT 

    Perform "TROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENT ".

    Trouble is fixed: INSPECTION END 

    Trouble is not fixed: Replace three way catalyst (manifold).

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