Secondary Air System, Checking

Secondary air system, checking (engine code ATW)
Following a cold start, the secondary air system helps to quickly heat the catalytic converter for quicker operating readiness.

Principle
Due to overenrichment of the mixture during the cold start phase, there is an increased amount of uncombusted carbon monoxide in the exhaust. Secondary Air Injection (AIR) improves secondary oxidation in the catalytic converter and therefore reduces emissions. The heat produced by secondary oxidation greatly reduces start-up time for the catalytic converter which significantly improving exhaust quality during the cold start phase.

Function:
^ In the cold start phase, the ECM -2- activates the secondary air pump 12- via the relay for secondary air pump -1-. Air is supplied to the combination valve for Secondary Air Injection (AIR) -10-.
^ The Secondary Air Injection (AIR) valve 3- is activated in parallel, which allows the vacuum to reach the combination valve for Secondary Air Injection (AIR) -10- and the vacuum diaphragm for boost pressure regulation 7-. The combination valve for Secondary Air Injection (AIR) thereby opens the path for secondary air to the exhaust channels of the cylinder head.
^ To prevent unnecessary heating, the secondary air is diverted past the turbocharger -7-. For this, the boost pressure regulation pressure unit opens the boost pressure valve. The pressure unit, designed as a double reservoir, has a vacuum connection for this on the intake side.

1 - Secondary Air Injection (AIR) pump relay J299-
2 - Motronic Engine Control Module (ECM) - J220-
3 - Secondary Air Injection (AIR) solenoid valve N1 12-
4 - Intake manifold
5 - Check valve
^ Installation position (light/dark side): Arrow points in direction of flow, as shown
6 - Vacuum reservoir
7 - Pressure unit for boost pressure regulation
8 Turbocharger
9 - Cylinder head
10 - Combination valve for secondary air injection (AIR)
11 - Air cleaner
12 - Secondary Air Injection (AIR) pump motor -V101-