How much does it cost to fix P0420?

Typical repair cost is $200–$2,500.

P0420 — Catalyst System Efficiency Below Threshold — Bank 1

Medium Severity · Emissions

OBD-II code P0420 means your vehicle's ECU detected: Catalyst System Efficiency Below Threshold — Bank 1. Below: causes, step-by-step fixes, and repair cost — free, no signup needed.

Drivable short-term but schedule a diagnosis soon. Prolonged driving can worsen the issue.

Typical Repair Cost

$200–$2,500

Parts + labor, national average

Severity

Medium

Schedule repair soon

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Common Causes of P0420

Failing catalytic converter
Bad O2 sensor
Engine misfires damaging cat
Oil burning into exhaust

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How to Fix Code P0420

Check for related misfires or O2 sensor codes first

Test upstream and downstream O2 sensors ($50–$200)

Inspect for exhaust leaks before cat

Replace catalytic converter if sensors confirm failure ($400–$2,500 depending on make)

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FAQ — Code P0420

What does OBD-II code P0420 mean?

P0420 means your vehicle's onboard computer detected: Catalyst System Efficiency Below Threshold — Bank 1. This is a medium-severity code in the Emissions category.

How much does it cost to fix code P0420?

Typical repair cost for P0420 is $200–$2,500 including parts and labor. Costs vary by vehicle make, model, and location. A free scan at AutoZone or O'Reilly is a good first step.

Can I drive my car with code P0420?

Code P0420 is generally safe for short trips, but have it diagnosed soon to prevent the problem from worsening.

What are the most common causes of P0420?

The most common causes are: Failing catalytic converter, Bad O2 sensor, Engine misfires damaging cat, Oil burning into exhaust. Always start with the cheapest diagnosis step before replacing parts.

Will code P0420 clear itself?

Code P0420 will clear itself after the underlying issue is fixed and the ECU completes several successful drive cycles. Clearing it without fixing the root cause only masks the problem temporarily.

Is P0420 showing on your car?

Enter your VIN for a free vehicle-specific report — recalls, specs, and market value. No signup required.

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Related Emissions Codes

P0400Exhaust Gas Recirculation Flow Malfunction P0401EGR Flow Insufficient P0402EGR Flow Excessive P0403EGR Control Circuit Malfunction P0404EGR Control Circuit Range/Performance P0410Secondary Air Injection System Malfunction

OBD-II code data is based on SAE J2012 standards and general repair industry data. Repair costs are national averages and vary by vehicle, location, and shop. Always consult a qualified mechanic for a diagnosis specific to your vehicle.