AUDI A4 1999 B5 / 1.G AWM Engine Secondary Air System Workshop Manual

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Secondary air system Secondary air system,
function/components

The secondary air system permits faster warm-up
and thus makes the catalytic converter ready for
operation sooner after cold starting.
Principle
Due to over-enrichment of the mixture in the cold
start phase, there is an increased amount of
unburned hydrocarbons in the exhaust gas. The
injection of secondary air improves the oxidation in
the catalytic converter and thus reduces emissions.
The heat produced by secondary oxidation reduces
start-up time for the catalytic converter therefore
improving the emission quality in the cold-running
phase.
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Function

During the cold running phase, the engine
control module -6- actuates the secondary air
injection pump -1- via the secondary air
injection pump relay -5-. Air reaches the
combination valve for the secondary air inlet -3-.
Parallel to this the secondary air inlet valve -8-
is actuated, which allows the vacuum to reach
the combination valve for secondary air inlet -3-.
The combination valve for secondary air inlet
thus allows the secondary air to enter the
exhaust ducts of the cylinder head -9-.
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1 -
Secondary Air Injection (AIR) Pump motor
-V101-
Location Fig. 2
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2 -
Air cleaner
3 -
Combination valve for secondary air inlet
Location Fig. 4
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4 -
Non-return valve
Position (light side/ dark side or direction of
arrow) as shown in illustration, arrow faces
in direction of flow
5 -
Secondary Air Injection (AIR) Pump relay -
J299- Location Fig. 3
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6 -
Engine Control Module -J220-
7 -
Vacuum reservoir
Location: In front left wheel housing
beneath wheel housing liner
8 -
Secondary Air Injection (AIR) Solenoid
valve -N112- Location Fig. 1
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9 -
Cylinder head
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Note:
The illustration shows bottom view of intake pipe. Fig. 1 Installation position Secondary Air Injection (AIR) valve -
N112-
Location: below intake pipe
1 - Recirculating valve for turbocharger -N249- (green connection)
2 - Secondary air injection valve -N112- (brown connection)

Fig. 2 Installation position for Secondary Air Injection (AIR)
Pump motor -V101-
Front right in engine compartment beneath air filter housing
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Fig. 3 Installation position Secondary Air Injection (AIR) Pump
relay -J299-
In E-box in plenum chamber
1 - Engine control module
2 - Secondary air pump relay -J299-
3 - Power supply relay for Motronic -J271-
4 - Fuse S130 for secondary air pump

Fig. 4 Combination valve for secondary air injection
Right rear on cylinder head
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Secondary Air Injection (AIR) Solenoid
valve -N112-, checking

Special tools and equipment

VAG 1526 A
VAG 1527 B
VAG 1594 A
VAG 1598/31
VAS 5051 with VAS 5051/1
- or
VAG 1551 with VAG 1551/3 A
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Test requirements:

Vehicle diagnostic, testing and information
system VAS 5051 or VAG 1551 Scan Tool
connected.

Test sequence

Note:
The secondary air injection solenoid valve -
N112- and the wiring connections are monitored
by the engine control module.

- Read out Diagnotic Trouble Code (DTC)
memory of engine control module.
If a DTC relating to the secondary air injection
solenoid valve -N112- is displayed:

Note:
The illustration shows bottom view of intake line. - Remove hoses from secondary air injection solenoid valve -N112- (-2-)
but leave electrical connector plugged in.
Location: below intake line
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- Connect auxiliary hose to valve connector marked with an arrow.
- Initiate output Diagnostic Test Mode (DTM) and activate secondary air
injection solenoid valve -N112-.
Output Diagnostic Test Mode Secondar
y air in
jection solenoid valve -N112-

Display:
If the injector does not click:
If valve does not open or close properly:
The valve should click ... ... and should open and close (check by blowing into the auxiliary
hose).
- Check internal resistance of valve.
- Replace secondary air injection solenoid valve -N112-.
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Checking internal resistance

- Disconnector connector of secondary air injection solenoid valve -
N112- (-Item 2-).

If specified value is not attained:
If specified value is attained: - Connect multimeter to injector to measure resistance.
Specified value: 27 to 30
- Replace secondary air injection solenoid valve -N112-.
- Check power supply.
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