OBD-II TROUBLE CODE GUIDE
P0420: Catalyst System Efficiency Below Threshold — Bank 1
The bank 1 catalyst shows less oxygen-storage performance than expected.
What P0420 means
The bank 1 catalyst shows less oxygen-storage performance than expected.
Common possible causes
- Exhaust leak
- Unresolved misfire or mixture problem
- Biased oxygen sensor or deteriorated converter
What to check first
Record all stored and pending codes and freeze-frame data before clearing anything. Inspect relevant wiring, connectors, hoses, fluid levels, and obvious damage. Use vehicle-specific service information and test the affected system before purchasing parts.
A code is not a parts order. Several faults can create the same code, and replacing the component named in a code description may not correct the underlying problem.
Look up P0420 for my vehicle