Main Catalyst Efficiency Below Threshold (Bank 2)

What this code means

The catalytic converter on bank 2 is not cleaning the exhaust as well as it should. This usually means the catalyst has degraded over time or an upstream problem is affecting it.

Symptoms

• Check engine light on
• Failed emissions test
• Slight loss of fuel economy

Common causes

• Worn or failed catalytic converter (bank 2)
• Faulty downstream oxygen sensor
• Exhaust leak near sensors
• Engine misfire or rich/lean condition

Diagnostic steps

1. Scan for other codes first (misfire, fuel trim)
2. Check for exhaust leaks around sensors
3. Compare upstream and downstream O2 sensor readings
4. Replace catalytic converter if sensors are good

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