LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Nissan-Datsun >> 2004 >> Sentra SE-R >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Qr25DE >> DTC P0420: Three Way Catalyst Function >> Diagnostic Procedure >> A/T Models ULEV And M/T Models
April 5, 2026: LEMON Manuals is launched! Read the announcement.

A/T Models ULEV And M/T Models

  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 Exhaust Gas Leak
      G00777917Courtesy 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 the following items. Refer to "BASIC INSPECTION ".

    Fig 2: Target Idle Speed & Ignition Timing Specifications
    G00777918Courtesy of NISSAN MOTOR CO., U.S.A.

    OK or NG 

    1. OK: GO TO 5.
    2. NG: Follow the Basic Inspection.
  5. CHECK INJECTORS 
    1. Refer to WIRING DIAGRAM  for Injectors.
    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.
      Fig 3: Checking Injectors
      G00777919Courtesy of NISSAN MOTOR CO., U.S.A.

      Battery voltage should exist. 

    OK or NG 

    1. OK: GO TO 6.
    2. NG: Perform "DIAGNOSTIC PROCEDURE ".
  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.
    6. Fig 4: Checking Ignition Spark
      G00777920Courtesy of NISSAN MOTOR CO., U.S.A.

    OK or NG 

    1. OK: GO TO 7.
    2. NG: Check ignition coil with power transistor and their circuit.

      Refer to "IGNITION SIGNAL ".

  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. 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 

    Refer to "TROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENT ".

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