DTC P0420 Or P0430: 3-Way Catalyst Function
The ECM monitors switching frequency ratio of front and rear HO2S. See Figure. A 3-way catalyst with high oxygen storage capacity indicates low switching frequency of rear HO2S. As oxygen storage capacity decreases, rear HO2S switching frequency increases. ECM then measures switching lag time between front and rear HO2S. Longer lag time indicates greater oxygen storage capacity. If lag time is within specified range, defective 3-way catalyst is indicated.
- Check HO2S Switching - Start engine and warm to operating temperature. Attach negative probe of voltmeter to ECM connector terminal No. 25 (engine ground). See Figure. Attach positive probe of voltmeter to ECM No. 50 (front right H02S), ECM No. 51 (front left H02S), ECM No. 56 (front right rear H02S) or ECM No. 57 (front left H02S). Raise engine speed to at least 2000 RPM and record voltage switching frequency. If voltage does not switch at least 5 times in 10 seconds, go to appropriate HO2S circuit test. If voltage switches as specified, go to next step.
- Check For Exhaust/Intake Air Leak - Visually inspect exhaust system for damage or leaks. Start engine and run at idle. Listen for exhaust leak prior to three way catalyst. Listen for intake air leak after MAF sensor location. Repair or replace faulty components or repair damage as required. If no problems exist, go to next step.
- 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, 104, 106, 109, 111, 113, 118 and 120. See Figure. If battery voltage does not exist, repair fault in appropriate circuit. If all injector circuits are okay, go to next step.
- 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.
- 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.