A P0420 diagnostic code on your 2021 Toyota Highlander indicates that Bank 1's catalytic converter efficiency has fallen below acceptable thresholds. The Highlander offers both 4-cylinder and V6 engine options with different exhaust configurations.
2021 Highlander Engine Options
- 2.5L 4-cylinder Hybrid: Single exhaust bank
- 3.5L V6: Dual exhaust banks - P0420 affects Bank 1
Common Causes
- Converter Degradation: Wear or contamination
- O2 Sensor Issues: Faulty sensors triggering false codes
- Exhaust Leaks: Air entering system
- Engine Problems: Misfires damaging converter
- Oil Consumption: Contaminating converter
V6 Bank Configuration
For V6 models, Bank 1 is typically the rear cylinder bank near the firewall. P0430 would indicate Bank 2 issues.