P0420

Catalyst System Efficiency Below Threshold Bank 1

P0420 - Catalyst system efficiency below threshold bank 1.: Last occurrence - maximum signal

Possible causes:
1. Oxygen sensor fault bank 1
2. Damaged/poisoned catalyst 1.

1. Oxygen sensor fault bank 1
- There is a catalyst efficiency fault. Check the oxygen sensors on the same cylinder bank for faults.
- Only if there are no other faults present should the catalyst be changed.

2. Damaged/poisoned catalyst 1.
- There is a catalyst efficiency fault. Check the oxygen sensors on the same cylinder bank for faults.
- Only if there are no other faults present should the catalyst be changed.