AUDI A4 1998 B5 / 1.G APB Engine Secondary Air System Workshop Manual

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Secondary air system The secondary air system results in quicker heating
and therefore earlier operating readiness of the
catalytic converter following cold start.
Principle
Due to over-enrichment of the mixture during the
cold start phase, there is an increased amount of
un-combusted 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, therefore improving
exhaust quality during the cold start phase
significantly.
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Function:

In the cold start phase, the ECM -4- activates
the secondary air pump -2- via the relay for
secondary air pump -3-. Air reaches the
combination valves for Secondary Air Injection
(AIR) -5- and -9-.
The Secondary Air Injection (AIR) valve -6- is
activated in parallel, which allows the vacuum to
reach the combination valves for Secondary Air
Injection (AIR) -5- and -9-. The appropriate
combination valve for Secondary Air Injection
(AIR) thereby opens the path for secondary air
to the exhaust channels of the cylinder head.
1 -
Secondary Air Injection (AIR) pump relay -
J299-
Removing and installing Page 26
-37
checking Page 26
-45
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2 -
Motronic Engine Control Module (ECM) -
J220-
3 -
Combination valve for secondary air
injection (AIR)
4 -
Secondary Air Injection (AIR) solenoid
valve -N112-
Installation position Fig. 1
5 -
Secondary Air Injection (AIR) pump motor
-V101-
Installation position Fig. 2
6 -
Check valve
Installation position (light/dark side): Arrow
points in direction of flow, as shown in
figure.
7 -
To Intake manifold
8 -
Combination valve for secondary air
injection (AIR)
9 -
Vacuum reservoir Installation location: Under wheel housing
liner in wheel housing
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Secondary Air Injection (AIR) system
components, removing and installing

The components for the Secondary Air Injection
(AIR) system are located under the air distributor
between the intake manifold and the plenum
chamber.
1 -
6 Nm
2 -
Secondary Air Injection (AIR) solenoid
valve -N112-
3 -
10 Nm
4 -
Large shim washer
For all 3 rubber bonded bushings at
bracket for Secondary Air Injection (AIR)
pump
5 -
Combination valve, left
6 -
Seal
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7 -
10 Nm
8 -
Secondary Air Injection (AIR) pump with
air filter attached
9 -
10 Nm
10 -
Seal
11 -
Combination valve, right
12 -
Bracket for Secondary Air Injection (AIR)
pump
Bolted to rear intake manifold.
13 -
10 Nm
14 -
Screw clamp
15 -
Connection tube Between Secondary Air Injection (AIR)
pump and combination valves
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Fig. 1 Installation location of Secondary Air Injection (AIR)
solenoid valve -N112-
Bolted to rear intake manifold at bracket below control modules
together with the connector for exhaust gas temperature (to the right
of the AIR motor) -3-.

Fig. 2 Installation position of Secondary Air Injection (AIR) pump
motor -V101-
At intake manifold, rear left -4-.
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Secondary Air Injection (AIR) solenoid
valve -N112-, removing and installing


- Remove bolts (arrows) and remove engine covers -A- and -B-.

- Remove air distributor (arrows).
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- Disconnect both connectors -2- from control modules for exhaust gas
temperature.
- Remove control modules from intake manifold and set wires aside.
- Secondary Air Injection (AIR) solenoid valve -N112- is secured to a
bracket below control modules for exhaust gas temperature sensor.
- Disconnect harness connector from valve and slide bracket off studs at
intake manifold with vacuum lines connected.
- Disconnect vacuum lines from Secondary Air Injection (AIR) solenoid
valve, remove valve from bracket.
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Secondary Air Injection (AIR) solenoid
valve -N112-, checking

Special tools and equipment

VAG 1526A
VAG 1527B
VAG 1594A
VAG 1598/31
VAS 5051
- or
VAG 1551 with VAG 1551/3A
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Installation location Installation locations-
Overview
Repair Manual, 2.7 Liter V6 5V BiTurbo Fuel
Injection & Ignition, Engine Code(s): APB, Repair Group 24


Test requirement:

Output Diagnostic Test Mode (DTM)
performed

Checking internal resistance

- Disconnect harness connector from Secondary
Air Injection (AIR) valve -N112-.

- Connect multimeter at valve for resistance measurement.

Specified value: 25 ... 35
- If specified value is not obtained, replace Secondary Air Injection (AIR)
solenoid valve -N112-.
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