DTC P0420 Or P0430: 3-Way Catalyst Function
The ECM monitors switching frequency ratio of front and rear HO2S. 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). Attach positive probe of voltmeter to ECM No. 50 (front right H02S), ECM No. 51 (front left H02S), ECM No. 56 (right rear H02S) or ECM No. 57 (left rear H02S). See Fig 2 or Figure . 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 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 and 113. See Figure. If battery voltage does not exist, repair fault in appropriate circuit. If all injector circuits are okay, go to next step.
- Check Components - Visually inspect exhaust system for damage or leaks and repair if necessary. Relieve fuel pressure and remove injector assembly. See REMOVE/INSTALL/OVERHAUL article. Do not remove fuel hose or injector from injector gallery. Disconnect CMP wiring harness connector. Turn ignition on. Verify fuel does not drip from injector(s). Replace any injector(s) that drip fuel. Perform FINAL CHECK.