P0420 Code — Catalytic Converter Efficiency Below Threshold (Easy Fix Guide)

P0420 is one of the most common error codes.

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Meaning

Your catalytic converter is not working efficiently.

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Common Causes

• Faulty O2 sensor
• Exhaust leak
• Worn catalytic converter
• Bad fuel quality
• Misfire damaging the catalytic

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Simple Fix Steps

1. Check for exhaust leak
2. Inspect O2 sensors (front & rear)
3. Check spark plugs and coils
4. Use high-quality fuel
5. If mileage > 200,000 km → catalytic may be worn out

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Temporary Fix

Use a catalytic cleaner fuel additive — works sometimes on minor blockages.