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Home >> Nissan-Datsun >> 2004 >> Sentra SE-R >> Repair and Diagnosis >> External Pages >> Different car >> Section 38 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0420: 3-Way Catalyst Function >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Nissan Altima. However, it is still accessible from the selected car via links, so may be relevant.
  1. Visually inspect exhaust system for damage. Start engine and let it idle. Check for exhaust leak prior to 3-way catalyst. Also, check for intake air leak after MAF sensor. If problem is found, repair as necessary. If problem is not found, go to next step.
  2. Check ignition timing and target idle speed. See ON-VEHICLE ADJUSTMENTS article. If ignition timing and target idle speed are okay, go to next step. If ignition timing and target idle speed are not okay, perform BASIC INSPECTION. See ON-VEHICLE ADJUSTMENTS article.
  3. Turn engine off. Turn ignition on. On 2.5L, measure voltage between ground and ECM terminals No. 101 (Red/Black wire), No. 102 (Red/White wire), No. 103 (Red/Yellow wire) and No. 104 (Red/Blue wire) by backprobing. See Figure and Figure . On 3.5L, measure voltage between ground and ECM terminals No. 1 (Red/Black wire), No. 2 (Red/White wire), No. 3 (Red/Yellow wire), No. 11 (Red/Blue wire), No. 12 (Blue/White wire) and No. 13 (Purple/Red wire) by backprobing. On all models, if battery voltage exists on all circuits, go to next step. If battery voltage does not exist on all circuits, repair appropriate injector circuit(s). See SYSTEM & COMPONENT TESTING article.
  4. Turn ignition off. Remove ignition coils from rocker covers. Connect a known-good spark plug to coil and ground spark plug end. Crank engine and check for spark. If spark exists at all coils, go to next step. If spark does not exist at any coil, repair ignition system. See SYSTEM & COMPONENT TESTING article.
  5. Turn ignition off. Remove injector assembly, keeping fuel hose and all injectors connected. Disconnect all ignition coil harness connectors. Turn ignition on. Verify fuel is not dripping from any injectors. Replace any injectors from which fuel is dripping. If all injectors are okay, go to next step.
  6. No problem is indicated at this time. Problem may be intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
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