Think of an oxygen sensor like a runner on a treadmill. When new, the runner can sprint and change speeds instantly in response to the coach's whistle. Over time, the runner gets older and slower. They still run, but their reaction time lags.
: The shutters remain closed during cold starts to help the engine reach operating temperature faster and improve aerodynamics. They open when the engine requires additional airflow to prevent overheating. 32ce00 bmw fixed
Allow air to cool the radiator when the engine is hot or the climate control is running. Think of an oxygen sensor like a runner on a treadmill