Catalyst System Efficiency Below Threshold (Bank 1)
Emission · Catalytic Converter
Your catalytic converter isn't cleaning exhaust gases efficiently enough. This code is common in vehicles over 80k miles and often appears after an upstream oxygen sensor failure or prolonged use of low-quality fuel. The converter's precious metal catalyst has degraded below the efficiency threshold your ECU expects.
- Worn or failing catalytic converterMost common
- Faulty O2 sensor (upstream or downstream)Common
- Exhaust leak near O2 sensor bungLess common
- Engine misfires contaminating converterLess common
Frequently asked questions
What does P0420 mean?
Your catalytic converter isn't cleaning exhaust gases efficiently enough. This code is common in vehicles over 80k miles and often appears after an upstream oxygen sensor failure or prolonged use of low-quality fuel. The converter's precious metal catalyst has degraded below the efficiency threshold your ECU expects.
Is P0420 serious?
Safe to drive short-term — fix within 2 weeks to avoid emissions failure.
How much does it cost to fix P0420?
Repair costs for P0420 range from $120 – $300 depending on the root cause and your vehicle.
Can I drive with P0420?
You can drive short distances but should have it repaired within 1-2 weeks to prevent further damage.