Secondary Air

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Secondary Air system function

The secondary air system is an emissions control device designed to decrease the warm-up time of the catalytic converters. If the catalytic converter warm-up time can be decreased, then the overall emissions output is also decreased. During startup the secondary air system reduces the HC and CO emissions, quickly increasing the exhaust temperature thus converting NOx emissions earlier.


Air is injected directly into the exhaust manifold just after the exhaust valves. Flow is created by the secondary air pump controlled via the DME control unit. The air is now directed into the exhaust manifold by a one-way valve designed to close when the secondary air pump is deactivated. An activation solenoid is used to control the operation of the one-way valve, the solenoid valve connects the one-way valve to engine vacuum to open the valve. The activation solenoid is controlled by the DME control unit. In some systems the activation solenoid is eliminate and replaced by a one-way valve activated by air pressure. The DME controls the timing of the activations of the air pump and solenoid valve to reduce the exhaust emissions.

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