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Home >> Nissan-Datsun >> 2003 >> Sentra Limited >> Repair and Diagnosis >> External Pages >> Different car >> Section 69 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold - Bank 1 Or DTC P0430: Catalyst System Efficiency Below Threshold - Bank 2 >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Nissan Xterra and 2002 Nissan Frontier. 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, target idle speed and closed throttle position switch adjustment by performing BASIC INSPECTION. See ON-VEHICLE ADJUSTMENTS article. Adjust as necessary. Go to next step.
  3. Turn engine off. Turn ignition on. On 2.4L models, measure voltage between ground and ECM terminals No. 102 (White/Black wire), No. 104 (White/Red wire), No. 109 (White/Blue wire) and No. 111 (White/Purple wire) by backprobing. See Figure . See Figure or Figure . On 3.3L models, measure voltage between ground and ECM terminals 102 (White/Black wire), No. 104 (White/Red wire), No. 106 (White/Green wire), No. 109 (White/Blue wire), No. 111 (White/Purple wire) and No. 113 (White 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. Disconnect ignition wire from spark plug. Connect a known-good spark plug to coil and ground spark plug end. Crank engine and check for spark. If spark exists on all cylinders, go to next step. If spark does not exist on any cylinder 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. Check for intermittent condition. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. If problem is found, repair as necessary. If problem is not found, replace 3-way catalyst.
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