Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Secondary air system: Function
During cold starting the secondary air system blows air in behind the exhaust valves. This produces an oxygen rich exhaust gas, causes afterburning and reduces the heating-up phase of the catalytic converter. Activation is performed by the Motronic Engine Control Module J220 via the Secondary Air Injection (AIR) pump relay J299 to the combi-valve.
Checking secondary air system → Secondary air system, checking .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.