Catalyst System Efficiency Below Threshold (Bank 1)

What This Means

The catalytic converter on bank 1 is not cleaning exhaust gases as effectively as it should. The downstream oxygen sensor is seeing readings too similar to the upstream sensor, meaning the converter is not doing its job of converting harmful emissions.

Common Symptoms

• Check engine light on
• Sulfur or rotten egg smell
• Reduced engine performance
• Failed emissions inspection

Common Causes

• Worn-out catalytic converter
• Engine misfire damaging the converter
• Oil or coolant contamination of the converter
• Exhaust leaks before or after the converter
• Faulty downstream O2 sensor giving false reading

Estimated Repair Cost