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Check Engine Light for Secondary Air Pump Malfunction

Model: BMW Serie 5 E39 - Years 1995-2003
Part: Warning light – error code

For cold starting a gasoline engine, a rich mixture is necessary, meaning an excess of fuel; however, until the catalytic converter reaches its operating temperature, which activates the Lambda control, large amounts of carbon monoxide and unburned hydrocarbons are produced. To reduce the formation of these harmful substances during cold starts, air is blown directly behind the exhaust valves into the manifold through the secondary air pump: this creates post-oxidation that converts the harmful substances into carbon dioxide and water. This system includes a vacuum-operated check valve and a switching solenoid: if either of these components fails, the check engine light illuminates on the dashboard, and a diagnostic tool can identify the fault based on the error code.

Updated on 9 February 2026 by ScegliAuto

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