Catalytic Converters
Catalytic Converters
Section titled “Catalytic Converters”The E46 330 uses two catalytic converters (pre-cat and main cat) to reduce exhaust emissions.
Function
Section titled “Function”- Pre-cat: Located close to manifold, heats up quickly for cold-start emissions
- Main cat: Primary catalytic converter, does bulk of conversion
Signs of Failure
Section titled “Signs of Failure”- Rotten egg smell (sulfur)
- Reduced power
- Check engine light (P0420, P0430 — catalyst efficiency below threshold)
- Rattling from inside converter (broken substrate)
Oxygen Sensors
Section titled “Oxygen Sensors”- Pre-cat O2 sensor: Monitors air/fuel ratio
- Post-cat O2 sensor: Monitors catalytic converter efficiency
- Total: 4 O2 sensors (2 per bank, pre and post cat)