What does code P0421 mean?
The catalytic converter on bank 1 does not reach proper efficiency during the warm-up phase.
OBD-II Code
P0421 — Warm Up Catalyst Efficiency Below Threshold (Bank 1
The catalytic converter on bank 1 does not reach proper efficiency during the warm-up phase.
Common symptoms
- Sulfur smell
- light exhaust smoke
- poor acceleration when cold
Possible causes
- Worn catalytic converter
- slow oxygen sensor response
- incorrect air-fuel mixture
Initial recommendation
Inspect oxygen sensors, verify engine mixture and catalytic converter warm-up efficiency.
Safety notice
This information is for guidance only and does not replace a physical vehicle inspection or diagnosis by a qualified mechanic. If the vehicle has severe power loss, smoke, a fuel odor, overheating, brake or steering problems, or any unsafe behavior, avoid driving it and seek professional inspection.
Analyze this code with MecaOBD
Use the app to combine code P0421 with your vehicle's actual symptoms for more complete diagnostic guidance.
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