P0421Toyota C-hrYears: 1996 - 2026
Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Reviewed by ASE Certified Technician
What does this mean?
Code P0421 indicates the Bank 1 catalytic converter is not reaching proper operating efficiency during the warm-up period.
Disclaimer: This diagnostic code is part of the standard OBD2 system and can apply to Toyota C-hr models manufactured from 1996 to 2026. However, please note that the presence of this specific code depends on your vehicle's exact engine configuration, options, and production year.
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Common Causes
Failing or clogged catalytic converter
Faulty oxygen (O2) sensor
Exhaust leak before oxygen sensor
Worn or fouled spark plugs
Symptoms to Watch For
- Check Engine Light is illuminated
- Failed emissions test
- Rotten egg smell (sulfur) from exhaust
- Decreased fuel economy