99 GMC Suburban P0420 and P0430 Codes: Are Two Bad Catalytic Converters the Cause?
I recently received diagnostic codes P0420 and P0430 on my 1999 GMC Suburban. Does this mean I have two faulty catalytic converters, or could there be another underlying issue causing these codes to appear? I'm looking for clarification on what these codes typically indicate and how to properly diagnose the root cause.
Check the oxygen (O2) sensor located at the very end of the exhaust system, after the catalytic converter. A faulty downstream O2 sensor can trigger both P0420 and P0430 codes. Also inspect the wiring harness connected to this sensor for any damage or breaks.