A P0420 diagnostic code on your 2021 Honda Pilot indicates that the Bank 1 catalytic converter efficiency has fallen below acceptable thresholds. The Pilot's V6 engine uses a dual-bank exhaust system, and P0420 specifically relates to Bank 1.
2021 Pilot Exhaust Configuration
The 2021 Pilot uses a 3.5L V6 engine with a dual exhaust system featuring two catalytic converters. P0420 affects Bank 1 only - if Bank 2 has issues, you would see P0430 instead.
Common Causes
- Converter Degradation: Age or contamination affecting efficiency
- O2 Sensor Issues: Bank 1 sensors malfunctioning
- Exhaust Leaks: Leaks affecting Bank 1 readings
- Engine Misfires: Cylinder misfires on Bank 1 damaging converter
- Oil Contamination: Internal leaks fouling converter
- Rich/Lean Conditions: Fuel system issues stressing converter