P0420 Code: What It Means & How to Fix It

What is the P0420 Code?

The P0420 diagnostic trouble code (DTC) indicates that your vehicle's catalytic converter is operating below its efficiency threshold.

Common Causes

• Failing Catalytic Converter - Converters wear out over time, typically lasting 100,000-150,000 miles.
• Faulty Oxygen Sensors - A bad O2 sensor can trigger false P0420 codes.
• Exhaust Leaks - Leaks before the catalytic converter can cause incorrect readings.
• Engine Misfires - Unburned fuel entering the converter can damage it.

Symptoms

• Check Engine Light illuminated
• Decreased fuel economy
• Failed emissions test
• Reduced engine performance

How to Fix

• Replace Oxygen Sensors ($50-150 each) - If sensors are faulty
• Repair Exhaust Leaks ($100-300) - Patch or replace leaking components
• Replace Catalytic Converter ($500-2,500) - If the converter is confirmed bad