Catalyst System Efficiency Below Threshold (Bank 1)
The oxygen storage capacity of the main catalytic converter on bank 1 has degraded below the OBD threshold. The downstream oxygen sensor signal increasingly mirrors the upstream sensor, indicating reduced conversion efficiency.
Affected components
- Catalytic converter
- Oxygen sensor upstream
- Oxygen sensor downstream
Common causes
- High likelihood: Catalyst aged or contaminated
- Medium likelihood: Downstream oxygen sensor drift
- Low likelihood: Exhaust leak before catalyst
- Low likelihood: Long-term misfire damage
Possible symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Related codes
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.