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Home >> Nissan-Datsun >> 2002 >> Sentra SE-R, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 2.5 >> Diagnostic Tests >> DTC P0420: 3-Way Catalyst Function >> Diagnostic Procedure
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Diagnostic Procedure

  1. Inspect exhaust system for damage. Repair exhaust system as necessary and retest system. If exhaust system is okay, go to next step.
  2. Start engine and run at idle. Check for exhaust leak in front of 3-way catalyst. Check intake system for leaks. Repair or replace faulty components as necessary and retest system. If problem does not exist, go to next step.
  3. Check ignition timing. See ON-VEHICLE ADJUSTMENTS article. If ignition timing is incorrect, adjust as necessary and retest system. If ignition timing is okay, go to next step.
    4. CAUTION: DO NOT use ECM ground terminals when measuring voltage.
  4. Turn engine off and turn ignition on. Measure voltage between ground and ECM terminals No. 101 (Red/Black wire), No. 103 (Yellow/Black wire), No. 105 (Green/Black wire) and No. 107 (Blue/Black wire) by backprobing. See Figure. If battery voltage exists on all circuits, go to next step. If battery voltage does not exist on all circuits, repair appropriate injector or circuit as necessary and retest system. See SYSTEM & COMPONENT TESTING article.
  5. Check for spark at misfiring cylinder(s). If spark is detected, go to next step. If no spark is detected, go to step  7.
  6. Measure resistance of spark plug wire at misfiring cylinder. Resistance should be 4.15-5.61 k/ohms per foot at 77°F (25°C). If resistance is not as specified, replace appropriate spark plug wire. If resistance is as specified, repair ignition coil, power transistor or related circuits as necessary and retest system. See SYSTEM & COMPONENT TESTING article.
    NOTE: Install NEW "O" rings on all fuel injectors once removed.
  7. Turn ignition off and allow engine to cool. Ensure no fire hazards exist and remove fuel injector assembly with fuel lines and harness connectors connected. Place a suitable cup under each fuel injector to collect fuel. Disconnect all ignition coil harness connectors. Turn ignition on. Verify fuel is not dripping from fuel injectors. If any injector is dripping, replace fuel injectors which are leaking. If no fuel injectors are leaking, go to next step.
  8. No problem is indicated at this time. Problem may be intermittent. See INTERMITTENTS in TROUBLESHOOTING - NO CODES article. If no problems are found, replace 3-way catalyst and retest system.
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