Secondary Air System, Principle and Function Audi TT 8N

Principle

Because of the over-enrichment of the mixture in the cold start phase, the percentage of unburned hydrocarbons in the exhaust gas is higher at that time. The injection of secondary air improves the post-oxidation in the catalytic converter and thus reduces pollutant emissions. The heat produced by the post-oxidation considerably shortens the start-up time of the catalytic converter and significantly enhances the emission quality in the cold-running phase.

Function

1. During the cold start phase (coolant temperature at + 15...+ 35° C) the secondary air system blows air behind the exhaust valves for approx. 65 seconds. This produces an oxygen-rich exhaust gas, causes afterburning and reduces the heating-up phase of the catalytic converter.
2. In addition, 20 seconds after each following engine start (until coolant temperature reaches 85° C), the secondary air system switches on for 5 seconds when at idling speed and is checked by the self-diagnosis.
3. The Secondary Air Injection (AIR) pump motor -V101- is actuated via the Motronic Engine Control Module (ECM) -J220-, the Secondary Air Injection (AIR) pump relay -J299-, the Secondary Air Injection (AIR) solenoid valve -N112-, the change-over valve and the combination valve.

Scheme 249

Note. For installed location for AIR pump relay -J299-. Refer to Installed location of Secondary Air Injection (AIR) pump relay -J299 .

1 - Intake manifold

2 - Vacuum unit for intake manifold change-over

3 - To intake manifold

4 - To fuel pressure regulator

5 - Combination valve for secondary air system

1. Removing and installing. Refer to «Combination valve for secondary air system, checking for proper operation and leakage»(ref-276269-S30056131112008010300000)

6 - Gasket

1. Replace

7 - Air channel

1. In cylinder head

8 - 10 Nm

9 - Connection for combination valve

10 - 5 Nm

11 - Pressure hose

1. Check for secure connection

12 - O-ring

1. Replace if damaged

13 - Connection

14 - Bracket

1. For AIR pump motor -V101
2. With support for sump

15 - 20 Nm

16 - Electrical connector

17 - Rubber bushing

18 - Secondary Air Injection (AIR) pump motor -V101

1. Removing and installing. Refer to «Secondary air injection pump, removing and installing»(ref-276269-S35561992282008010300000)

19 - Air cleaner

1. Clean if dirty

20 - Retaining clamp

21 - Intake hose

1. Check for secure connection

22 - Non-return valve

1. Installed position (light side/dark side): as shown in illustration; arrow indicates direction of flow

23 - Electrical connector

24 - Intake manifold change-over valve -N156

25 - Secondary Air Injection (AIR) solenoid valve -N112

26 - Vacuum reservoir

Scheme 250

Beneath cover on left at bulkhead

Note. To remove the protective cover, disconnect the relay at the bulkhead and lower. If necessary, unplug connector at Mass Air Flow sensor.