Emissions
Catalytic Converter
The catalytic converter turns harmful exhaust gases into less harmful ones.
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Emissions flow
Interactive — tap a partTap a part to see how it fits in the system.
What it does
- Converts CO, HC and NOx into CO₂, water and nitrogen
- Uses precious-metal catalysts (platinum, palladium, rhodium)
- Monitored by downstream O2 sensors
When it fails
- P0420 / P0430 codes
- Failed emissions test
- Rattling from a broken core
- Reduced power from a blocked catalyst
How to diagnose
- Compare upstream and downstream O2 activity
- Fix misfires and rich conditions first
- Measure exhaust backpressure
- Check the core rattles
Maintenance
- Never ignore a flashing check engine light — misfires destroy catalysts
- Use correct fuel (unleaded!)
- Fix oil consumption that coats the catalyst
Use the diagnosis order. When a part fails, confirm each hypothesis with measurements before replacing anything — codes and symptoms overlap.
Related part
Oxygen Sensor (O2 / Lambda)
The oxygen sensor measures exhaust oxygen so the ECU can fine-tune the air-fuel mixture.