Secondary air (only B234i for SE and US)
| Secondary air (only B234i for SE and US) |
To get the catalytic converter working as soon as possible after a cold start, ambient air is pumped into the exhaust manifold where the oxygen in the air starts a chemical combustion process together with CO, HC and NOx pollutants, thus generating heat.
About ten seconds after the engine fires, the secondary air injection pump starts and a solenoid valve opens the passage leading to the exhaust manifold.
Since this process is dependent on both time and temperature, the solenoid valve closes and the pump stops either when a maximum of 120 seconds has elapsed or when engine temperature reaches 70°C (158°F), whichever occurs first.
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