Catalyst System Efficiency Below Threshold Bank 1

Likely causes

• Worn-out catalytic converter
• Faulty downstream (rear) oxygen sensor
• Exhaust leak near the sensors
• Ongoing misfire or oil burning that damaged the converter

What to check first

Fix any misfire or exhaust leak first and check the rear oxygen sensor before buying a converter. An old car with this code may be worth more sold as-is than repaired.

Typical repair cost

Independent-shop parts and labor for the usual fix. Your price depends on the actual cause and the vehicle.

Next step