The secondary air injection system (AIS), also called an air pump, is a key component of a vehicle’s anti-pollution system. Its role is crucial for reducing harmful emissions during startup, when the catalytic converter has not yet reached its optimal operating temperature.
What is the function of the secondary air injection system (AIS)?
The AIS’s main mission is to inject fresh air directly into the exhaust gas stream, upstream of the catalytic converter. This injection of oxygen allows for the continued combustion of unburned fuel and residual hydrocarbons exiting the engine. This after-combustion has two major beneficial effects: it significantly reduces polluting emissions and it helps the catalytic converter heat up more quickly, thereby improving its efficiency from the very first moments after startup.
The different types of AIS systems
There are primarily two architectures for these systems. The first type uses a mechanical air pump, driven by the crankshaft via a belt, which pulses air directly into the exhaust. The second, more modern type, is the pulsed aspiration system. This one does not have a mechanical pump; instead, it uses the depression waves created in the exhaust manifold to draw in ambient air through a valve and route it to the catalytic converter.
Common failure symptoms and causes
A failure of the AIS is often indicated by the illumination of the check engine light and the storage of fault codes (such as P0410, P0411…). One might also observe an increase in polluting emissions during technical inspections, abnormal bearing noises (if the pump is seized or loose), or a minor loss of power. The most frequent failures involve the air pump itself failing, the check valve sticking, the solenoid valves malfunctioning, or the hoses and ducts becoming clogged or punctured.
Conclusion
The secondary air injection system is an essential element for complying with anti-pollution standards. Its proper functioning is crucial for minimizing the vehicle’s environmental impact, especially during cold-start phases. Therefore, regular maintenance and prompt repair in case of a fault are paramount.