Audi AMB Service Manual page 578

ENGINE 1.8 Liter 4-Cyl. 5V Turbo Engine Mechanical, Engine Code(s): AMB
Listen for noise at connection points of cylinder head/manifold, manifold/turbocharger,
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turbocharger/catalytic converter etc., to locate any leaks.
Correct any leaks that are found.
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SECONDARY AIR SYSTEM, CHECKING
Secondary air system, checking
The secondary air system is designed to enable the catalytic converter to heat up and reach its operating
temperature more quickly after a cold start.
Principle of operation
Due to extra mixture enrichment during the cold-start phase, an increased amount of unburned hydrocarbons is
present in the exhaust gas. The secondary air system improves the oxidation process in the catalytic converter
thereby reducing toxic emissions. The heat generated by oxidation accelerates the "light off" of the catalytic
converter and significantly improves exhaust gas quality during warm-up.
Function
After a cold start, the engine control module - 6 - activates the secondary air injection pump - 1 - via the
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secondary air injection pump relay - 5 - , and air is fed to the secondary air combination valve - 3 -.
At the same time, the system activates the secondary air injection solenoid valve - 8 - which supplies
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vacuum to the secondary air combination valve - 3 -. The relevant combination valve opens a passage for
the secondary air injection system to supply air to exhaust ports in the cylinder head.
2005 Audi A4 Quattro
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