A P0420 diagnostic code on your 2021 Toyota Sienna indicates that the catalytic converter efficiency has fallen below acceptable thresholds. The completely redesigned 2021 Sienna is hybrid-only with a new powertrain.
2021 Sienna Hybrid System
The 2021 Sienna uses a 2.5L 4-cylinder hybrid system producing 245 hp combined. This replaced the previous V6 - all 2021+ Siennas are hybrids with single exhaust banks.
Hybrid-Specific Considerations
- Intermittent Engine: Engine starts/stops frequently
- Lower Exhaust Temps: Less constant heat than V6
- Electric-Only Operation: Engine may not run in some conditions
Common Causes
- Converter Issues: Wear or contamination
- O2 Sensor Problems: False codes from sensors
- Hybrid Operation: System affecting converter function
- Exhaust Leaks: Air entering system