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DTC P0420: 3-Way Catalyst Function

  1. Check For Exhaust/Intake Air Leak  - Visually inspect exhaust system for damage or leaks. Start engine and allow to idle. Listen for exhaust leak upstream of three way catalyst. Listen for intake air leak after MAF sensor location. Repair or replace faulty components as necessary. If no faults are present, go to next step.
  2. Check Injectors  - Turn ignition off. Disconnect ECM harness connector. Disconnect injector harness connectors. Turn ignition on. Using a voltmeter, measure voltage between ground and ECM harness connector terminals No. 102 (White/Black wire), 104 (White/Red wire), 107 (White/Blue wire) and 109 (White/Green wire). See Figure. If battery voltage is present, injector circuits are okay, go to next step. If battery voltage is not present, check for fault in circuit. If no faults are present, go to FUEL SYSTEM in SYSTEM/COMPONENT TESTS article.
  3. Turn ignition off. Reconnect injector harness connectors. Remove injector assembly, keeping fuel hose and all injectors connected. Disconnect CMP sensor harness connector. 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.
  4. Disconnect and reconnect harness connectors in circuit. Check ECM pin terminals for damage or corrosion. Reconnect ECM harness connector and retest. If problems still exist, replace three way catalyst.
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