Diagnostic Aids
Check for any of the following conditions:
- A contaminated or malfunctioning HO2S can cause inaccurate sensor readings. For checks of HO2S, see DIAGNOSTIC AIDS in DTC P0130.
- Observe HO2S 1 voltage and fuel trim readings with a scan tool. If HO2S 1 voltage is fixed low, while fuel trim is constantly high, check Mass Air Flow (MAF) sensor signal circuit for resistance. High circuit resistance can cause sensor to read a lower volume of air than actual, resulting in a lean fueling condition. This lean fueling condition can cause HO2S 2 voltage to be fixed low, causing DTC P0420 diagnostic to fail.
- A damaged HO2S wiring harness. Check HO2S wiring harnesses for damage and repair as necessary.
- If a DTC P0420 is intermittent, driving vehicle under conditions outlined in Inspection/Maintenance (I/M) section can verify whether fault is present. See INSPECTION/MAINTENANCE CATALYST SYSTEM SET PROCEDURE under INSPECTION/MAINTENANCE PROCEDURES.
- After returning to an idle, the HO2S 1 signal may stay rich or lean for several seconds, causing the test to be delayed.
A catalytic converter failure may be caused by any of the following conditions:
- An engine misfire.
- An inadequate secondary ignition voltage.
- Any excessive engine oil or engine coolant consumption.
- A rich engine fueling.