Secondary air system components, removing and installing
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 the extra mixture enrichment during the cold-start phase, an increased amount of unburnt hydrocarbons is carried in the exhaust gas. The secondary air system improves the afterburning (oxidation) process in the catalytic converter, and in this way reduces 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 engine control module -2-activates secondary air pump -12- via secondary air pump relay -1-, and air is fed to mechanical secondary air valve -10- (combination valve).
- At the same time, the system activates secondary air inlet valve -3-, which supplies vacuum to mechanical secondary air valve -10- and to pressure unit -7- for charge air pressure control.
- In this way, the mechanical secondary air valve opens a passage for the secondary air system to supply air to the exhaust ports in the cylinder head.
- To avoid generating unnecessary heat, the secondary air is channelled past the turbocharger. This is achieved by means of the pressure unit for charge air pressure control, which opens the charge air pressure control valve. To perform this function, the pressure unit is designed as a two-way pneumatic unit with an additional vacuum connection on the "pull-in" side.
1 - Secondary Air Injection (AIR) Pump Relay -J299-
2 - Motronic Engine Control Module (ECM) -J220-
3 - Secondary Air Injection (AIR) Solenoid Valve -N112-
4 - Intake manifold
5 - Non-return valve
- Installation position (light side/dark side) as shown in illustration. Arrow indicates direction of flow
6 - Vacuum reservoir
- Bolted to cylinder head cover
7 - Pressure unit for charge air pressure control
8 - Turbocharger
- Testing charge air pressure. Refer to Turbocharger and wastegate bypass regulator valve, testing
9 - Cylinder head
10 - Mechanical secondary air valve (combination valve)
- For secondary air system
11 - Air cleaner
12 - Secondary Air Injection (AIR) Pump Motor -V101-