Tài Liệu Hệ Thống Xử Lý Khí Thải Selective Catalytic Reduction SCR Động Cơ Diesel Audi

Self Study Programme 622
For internal use only

Second generation Audi clean diesel

Audi
Service Training


The SCR system - the key to achieving the tougher EU 6-1 (W), BIN 5, Tier 2 and LEV III emission standards
Reducing the nitrous oxide content (NOx) in exhaust emissions is a
global challenge facing automobile manufacturers, who are
required to meet the new statutory limits set by the Euro 6 standard and equivalent international regulations on exhaust emission
limits.
A modern "Selective Catalytic Reduction" (SCR) emission control
system utilises the chemical synthesis product of urea (AdBlue®)
to reduce NOx emissions.
In SCR systems, AdBlue® reacts with the NOx emissions to produce
water vapour and nitrogen. NOx is short for nitrous oxide gases;
they occur during the combustion process in diesel engines and are
reduced by means of SCR technology. ''

1)

AdBlue® is manufactured by a solution of a chemical called urea
(also called carbamide) in water. Urea is a synthetic product which
usually is made from natural gas and used in fertilizers, plastics
and cosmetics. AdBlue® is not made from recycled agricultural
products. For exhaust gas aftertreatment in the AdBlue® SCR
system, the exhaust system requires additional components such
as the heated catalyst1), the water-cooled metering valve, the

diesel particulate filter with integrated DeNOx catalytic converter
and the ammonia blocking catalytic converter.
AdBlue® is a registered trademark of Verband der Automobilindustrie (VDA).

Installed in a limited number of models only.

622_023

Learning objectives of this self study programme:
This Self Study Programme describes the design and function of an
exhaust gas aftertreatment system adapted for the use of AdBlue®
reducing agent. Once you have completed this Self Study Programme you will be able to answer the following questions:

2

• What is the function of the heated catalyst?
• Which new sensors are integrated in the reduction system?
• Why does the exhaust gas temperature have to be relatively
high?
• What is the function of the ammonia blocking catalytic converter?

622_002


Contents
Introduction
Emission standard ___________________________________________________________________________________________________________________________________________ 4
Audi models based on the Modular Longitudinal Matrix (MLB) with SCR system _____________________________________________________________________ 5

Exhaust gas aftertreatment by an SCR system

Basic design (overall system) _______________________________________________________________________________________________________________________________ 6

Exhaust systems
Introduction __________________________________________________________________________________________________________________________________________________ 8
1.6l / 2.0l TDI engine (EA288) _ ____________________________________________________________________________________________________________________________ 8
3.0l V6 TDI engine __________________________________________________________________________________________________________________________________________ 12
4.2l V8 TDI engine __________________________________________________________________________________________________________________________________________ 16

Fuel and reducing agent tank
Reducing agent tank ________________________________________________________________________________________________________________________________________ 18
Audi Q7 _______________________________________________________________________________________________________________________________________________________ 18
Audi A6 ’11 and Audi A7 Sportback _______________________________________________________________________________________________________________________ 20
Audi A4 ’14 __________________________________________________________________________________________________________________________________________________ 22
Audi A8 ’10 and Audi A8 ’14 _______________________________________________________________________________________________________________________________ 24
Swirlpot in active tank ______________________________________________________________________________________________________________________________________ 27

Sensors and actuators
System overview (shown using the 3.0l V6 TDI engine as an example) _______________________________________________________________________________ 28
Reducing agent pump V437 _______________________________________________________________________________________________________________________________ 30
Reducing agent tank sender G684 (level sender) ________________________________________________________________________________________________________ 31
Particulate sensor G784 with control unit _______________________________________________________________________________________________________________ 32
Reducing agent injector N474 (metering valve) _________________________________________________________________________________________________________ 32

Display strategy
Overview _____________________________________________________________________________________________________________________________________________________ 35
Messages relating to reducing agent fill level ___________________________________________________________________________________________________________ 36
Fault warnings _______________________________________________________________________________________________________________________________________________ 37

Service
Tools __________________________________________________________________________________________________________________________________________________________ 38

Annex
Self Study Programmes ____________________________________________________________________________________________________________________________________ 39

The Self Study Programme teaches a basic knowledge of the design and functions of new models, new automotive components or new technologies.
It is not a Repair Manual! Figures are given for explanatory purposes only and refer to the data valid at the
time of preparation of the SSP. This content is not updated.
For further information on maintenance and repair work, always refer to the current technical literature.

Note

Reference

3


Introduction
Emission standard
The emission standard for motor vehicles limits sets out limits for
carbon monoxide (CO), nitrous oxide (NOx), hydrocarbons (HC) and
particulate matter (PM) and subdivides vehicles thus into emission
classes. Specific key numbers are assigned and used, for instance,
to calculate road tax and to classify vehicles for low emission
zones. Emission limits vary according to engine type (petrol or
diesel engine) and vehicle type.

They are subject to ongoing tightening within the European region.
The values are measured in type tests within the driving cycle, and
the vehicle manufacturer has to guarantee the compliance with
these limits for a specified period of time and mileage. This is

achieved by in-service monitoring and by carrying out recalls in
case of systematic faults. Some vehicles are subject to limits on
evaporative fuel emissions and mandatory On-Board Diagnostics
(OBD).

Emission limits from the emission standards

European Union

USA

Japan

in %

Particulate matter (PM)

Nitrous oxides (NOx)

Nitrous oxides (NOx)

Limits in g/mi

Limits in g/mi

in %

Hydrocarbons (HC) and nitrous oxides (NOx)

in %

Carbon monoxide (CO)

Limits in g/km

622_003

Abbreviations
LEV
ULEV
SULEV
BIN 5
4

Low Emission Vehicle
Ultra Low Emission Vehicle
Super Ultra Low Emission Vehicle
Emission standard for California and other US states

The term "BIN" stems from the word "bag"; this is because the
exhaust gases are collected in bags during emission tests and
analysed. There are 10 categories ranging from BIN 10 (highest
emissions) to BIN 1 (lowest emisisons).


Phase-in dates of EU emission standards for diesel engines

New types

New vehicles

EU 5

EU 5

EU 5

EU 6

EU 6

EU 6

EU 6

EU 6

A

F

J

N

Q

T

W

ZA1)

from

01.09.2009 01.09.2011 01.09.2011 –

–

–

01.09.2014 01.09.2017

to

31.08.2011 31.08.2014 31.08.2014 –

–

–

31.08.2017 –

from

01.01.2011 01.01.2013 01.01.2014 –

–

–

01.09.2015 01.09.2018

to

31.12.2012 31.12.2013 31.05.2015 31.12.2012 31.12.2013 31.08.2015 31.08.2018 –

Emission limits

EU 5 a

EU 5 b

EU 5 b

EU 6 a

EU 6 b

EU 6 b

EU 6 b

EU 6 c

OBD standard

EU 5

EU 5

EU 5 +

EU 6

EU 6

EU 6 +

EU 6-1

EU 6-2

1)

at planning stage

Audi models based on the Modular Longitudinal Matrix (MLB) with SCR system

622_014

A4 ’14
A5 ’14

Q5

A6 ’14
A7 Sportback

Q7

A8 ’13

A8 ’14

Engine type

2.0l R4 TDI
3.0l V6 TDI

2.0l R4 TDI
3.0l V6 TDI

2.0l R4 TDI
3.0l V6 TDI

3.0l V6 MPI

3.0l V6 MPI
4.2l V8 TDI

3.0l V6 MPI
4.2l V8 TDI

SCR tank system
manufacturer

Inergy Gen. II

Inergy Gen. II

Inergy Gen. I

Inergy Gen. II

Inergy Gen. I

Inergy Gen. II

Inergy Gen. II
Röchling

Reducing agent
active tank

x

x

x

x

x

x

Reducing agent
passive tank

x

AdBlue®
capacity

20 litres

x
22 litres

17 litres

23 litres

x
20 litres

27 litres

Reference
For information on the design and function of the SCR system in the Audi A3 saloon (USA), refer to Self Study Programme
625 "Audi A3 saloon".

5


Exhaust gas aftertreatment by an SCR system
Basic design (overall system)
Exhaust gas temperature sender 2
(upstream of oxidising catalytic converter)
G448

Oxygen sensor
G39

Reducing agent injector
N474 (water cooled)

Engine control unit
J623

Oxidising catalytic converter
with catalyst heater1)

SCR-coated diesel particulate filter

NOx sender 2 with control unit
G687

Ammonia blocking
catalytic converter

Catalyst heater control unit 11)
J1021

Components
The exhaust gas aftertreatment system comprises the reducing
agent tank system together with the water-cooled reducing agent
injector, a close-coupled heated catalyst1), an SCR-coated diesel
particulate filter and an ammonia blocking catalytic converter
located upstream of the main silencers.

1)

6

Installed in a limited number of models only.

Multiple temperature sensors are integrated in the exhaust system
upstream and downstream of the turbocharger together with the
oxidising catalytic converter, the diesel particulate filter, the
oxygen sensor and the NOx sender. The exhaust aftertreatment
process is monitored with the aid of the various sensors.


Task of the SCR system
In the first stage, emissions and fuel consumption are reduced by
minimising friction; in the second stage, emissions are minimised
by the exhaust gas aftertreatment system.

To achieve the EU 6 emission limits, new components, sensors and
actuators are used to minimise nitrous oxide emissions in addition
to the familiar AdBlue® reducing agent.

Reducing agent
filler neck

Reducing agent metering
system control unit
J880

Swirlpot with reducing
agent pump
V437

Heater metering line

Reducing agent
transfer pump
V436

Reducing agent
active tank

Reducing agent
passive tank

622_025

7


Exhaust systems
Introduction
To meet the requisite emission standards, modern exhaust
systems are no longer configured simply as silenced exhaust
systems, but as exhaust gas treatment and monitoring systems.
They comprise:

The exhaust systems has the following sensors:
• Oxygen sensors

• NOx sensors
• Differential pressure sensors

• Oxidising catalytic converter with/without catalyst heater1)
• SCR-coated diesel particulate filter
• Ammonia blocking catalytic converter

In addition, there are several temperature sensors which monitor
the temperature levels in the exhaust system.

The complex open and closed-loop control functions have been
integrated into the engine control unit.
1)

Installed in a limited number of models only.

1.6l / 2.0l TDI engine (EA288)

Exhaust gas temperature sender 4
(downstream of diesel particulate filter)
G648
Flexible pipe

Ammonia blocking catalytic converter, see "Ammonia blocking
catalytic converter" on page 11

Exhaust gas treatment module, see
"Exhaust gas treatment module with
SCR system" on page 10

Engine modifications
To meet the EU 6 requirements, the existing 2.0l and 1.6l TDI
engines have been upgraded to include the following components:
•
•
•
•

Variable valve timing
High pressure exhaust recirculation
Cylinder pressure control system
2000 bar injection system

Exhaust flap control unit
J883

622_006

Reference
The design and function of engines from the Modular Diesel System (EA288) are explained in Self Study Programme 608
"Audi 1.6l / 2.0l 4-cylinder TDI engines".

8


Exhaust gas treatment module

Versions

To achieve the EU 6 emission limits, an NOx aftertreatment system

will be integrated into the close-coupled exhaust gas treatment
module from the EU 5 engine together with the oxidising catalytic
converter and the coated particulate filter.

Depending on model version, a distinction will be made in future
between two EU 6 variants of the close-coupled exhaust gas
treatment module:

Achieving the EU 6 emission limits requires the use of a Selective
Catalytic Reduction (SCR) system.

• System with NOx accumulator catalyst (NSK) for smaller and
lighter vehicles based on the Modular Transverse Matrix (MQB)
• System with Selective Catalytic Reduction (SCR) for vehicles
based on the Modular Longitudinal Matrix (MLB) with a larger
flywheel mass (EU 6 heavy duty)

Overview

Exhaust gas recirculation servomotor 2
V339

EGR valve

EGR cooler

Exhaust gas treatment module
Turbocharger

622_028

9


Exhaust gas treatment module with SCR system
The substrate of the close-coupled exhaust gas treatment module
is made of metal, enabling the module to reach its operating
termperature more quickly. This metal body is coated with a
substrate of metal oxides, e.g. aluminium oxide, with additional
layers of platinum and palladium. These precious metals act as
catalysts for hydrocarbons and carbon monoxide.
Integrating the SCR coating into the particulate filter using copper
zeolite enables the system to be positioned close to the engine.
After cold-starting the engine, the operating temperature of the
SCR catalyst is reached more quickly and maintained for longer
during low-load vehicle operation.

Additional engine modifications are required for heating the
catalytic converter. The reducing agent injector N474 is integrated
directly downstream of the oxidising catalytic converter and above
the transition funnel, with the result that the entire volume in the
funnel is available for carburetion.
Since air cooling is no longer sufficient due to the high thermal
load, the reducing agent injector has a coolant jacket which, in
addition to the valve, protects the electrical connection against
overheating.
The reducing agent injector is integrated in the low-temperature
circuit of the engine cooling system, see page 34.

Design

Exhaust gas temperature sender 2
G448

Reducing agent injector
N474 (water cooled)

Exhaust gas temperature sender 3
G495

Oxygen sensor
G39

NOx sender
G295

Turbocharger

Mixer

Oxidising catalytic converter
Exhaust gas temperature sender 1
G235
Differential pressure sender
G505

Connection for exhaust gas pressure sensor 1
G450

SCR-coated diesel particulate filter

622_022
10


Ammonia blocking catalytic converter
An ammonia blocking catalytic converter with a combined SCR and
oxidising catalyst coating is located downstream of the SCR-coated
diesel particulate filter and performs two tasks:

Its second task is to ensure that no NH3 leaves the exhaust system.
During this process, NH3 is oxidised to N2 and H2O.

Its first task is to oxidise the carbon monoxide (CO) produced
during soot regeneration to carbon dioxide (CO2) through reaction
with the precious metal-containing coating.

Design and sensors

Exhaust pipe from exhaust gas treatment module

Ammonia blocking catalytic converter

Exhaust flap control unit
J883

622_021

Exhaust valve control unit J883
The task of the control unit is to generate a slight backpressure
downstream of the diesel particulate filter by means of a motorised exhaust gas flap.

This produces an excess pressure of approx. 30 – 40 mbar downstream of the particulate filter relative to the exhaust pressure
downstream of the exhaust flap. This excess pressure results in a
positive flow gradient (purging rate) in the EGR cooler and in the
downstream EGR valve. The flow of recirculated exhaust gas is
controlled (mapped) by the EGR valve. This backpressure is measured by exhaust gas pressure sensor 1 G450.

The 73° operating range of the exhaust flap is defined by:
• the exhaust pressure downstream of the exhaust flap
• the nominal exhaust pressure upstream of the exhaust flap
• the mass flow through the exhaust flap
In the event of failure of exhaust gas recirculation servomotor 2
V339, the exhaust valve control unit J883 takes on the task of
controlling the exhaust gas recirculation rate.

11


3.0l V6 TDI engine
What state-of-the-art diesel and direct injection petrol engines
have in common are ever-decreasing exhaust gas temperatures.
Automatic start-stop systems, regular intermittent operation of
compact internal combustion engines, or the more effective
conversion of combustion energy to mechanical drive power often
result in temperatures below the light-off temperature of the
catalytic converter.

The exhaust gas treatment module of the 3.0l V6 TDI engine has
been modified to meet the EU 6 (W) emission standard.
To make use of heat flow, the components of the exhaust gas
treatment module have been fitted close to the engine.

Overview

Exhaust gas temperature sender 2
(upstream of oxidising catalytic
converter) G448

Oxidising catalytic converter

Connection for differential pressure sensor
downstream of diesel particulate filter
Exhaust gas temperature sender 4 (downstream of
diesel particulate filter) G648

Oxygen sensor
G39
SCR-coated diesel particulate filter, see
"Oxidising catalytic converter and diesel
particulate filter" on page 14

Connection for differential
pressure sensor upstream
of diesel particulate filter
Connection for catalytic
converter heater 11)
Z119

1)

Installed in a limited number of models only.

12

Reducing agent injector
N474 (water cooled)


Sensors and connections on the diesel particulate filter
Exhaust gas temperature sender 2

Exhaust gas temperature sender 2 G448 and exhaust gas tem(upstream of oxidising catalytic converter)
perature sender 3 G495 are used, respectively, upstream and
G448
Oxygen sensor
downstream of the oxidising catalytic converter in order to
G39
monitor the operating temperature of the oxidising catalytic
converter. The values measured by both exhaust gas temperature sensors are also important variables for the regenConnection for differential pressure sensor
downstream of diesel particulate filter
eration of the diesel particulate filter. To determine the
load on the particulate sensor, the exhaust pressure is
measured upstream and downstream of the particulate
filter and not against atmospheric pressure.
Exhaust gas temperature sender 4 G648 monitors the
regeneration temperature.

Connection for exhaust gas temperature
sender 3 (downstream of oxidising catalytic converter) G495

Connection for differential pressure sensor

upstream of diesel particulate filter
622_046

NOx sender 2
G687

Ammonia blocking catalytic converter, see
"Ammonia blocking catalytic converter"
on page 15

622_005

13


Oxidising catalytic converter and diesel particulate filter
In some models, an electric heating plate1) has been integrated
into the oxidising catalytic converter to enable the oxidation
catalyst reach its light-off temperature more quickly. The heated
catalyst1) consists of a thin sheet of wound metal substrate, which
is installed upstream of the catalytic converter and energised as
required.

The exhaust gases are additionally heated with 500 watts of power
at cold start, after which the heating plate1) is energised at low
engine load (partial load) in order to maintain the temperature of
the catalytic converter.

Overview
Oxygen sensor

G39

Oxidising catalytic converter

Exhaust gas temperature sender 2
(upstream of oxidising catalytic
converter) G448

Connection for differential pressure sensor
downstream of diesel particulate filter

Reducing agent injector
N474 (water cooled)

Mixer
Connection for differential
pressure sensor upstream of
diesel particulate filter

Exhaust gas temperature sender 4
(downstream of diesel particulate
filter) G648

SCR-coated diesel
particulate filter

Heating plate1)

Connection for catalytic
converter heater 11)

Z119

Exhaust pipe to
ammonia blocking
catalytic converter

622_020
1)

Installed in a limited number of models only.

14


Ammonia blocking catalytic converter
An ammonia blocking catalytic converter is used in place of the
previous DeNOx catalytic converter. Now, an ammonia blocking
catalytic converter with a combined SCR and oxidation catalyst
coating is installed downstream of the SCR-coated diesel particulate filter and performs the following two tasks:

The second task of the ammonia blocking catalytic converter is to
ensure that no NH3 leaves the exhaust system. During this process,
NH3 is oxidised to N2 and H2O.

First, to oxidise the carbon monoxide (CO) produced during soot
regeneration to carbon dioxide (CO2) through reaction with the
precious metal-containing coating.

Design and sensors

Ammonia blocking cat

NOx sender 2
G687

622_024

15


4.2l V8 TDI engine
In the large-displacement 4.2l V8 TDI engine, an oxidising catalytic
converter with a 500 watts heating plate is fitted in each exhaust
pipe. This means that an oxygen sensor and an exhaust gas temperature sensor are installed upstream and downstream, respectively, of the oxidising catalytic converter.
Both exhaust pipes subsequently merge into one.

To ensure the even distribution of reducing agent via a mixer, the
air-cooled metering valve is installed in the most favourable
position. The exhaust system then splits again in order to accommodate the two SCR-coated diesel particulate filters. Two exhaust
gas temperature sensors located at the outlet of the diesel particulate filter monitor the regeneration temperature.

Overview
Oxygen sensor
G39

Connection of catalytic
converter heater 1
Z119

Exhaust gas temperature sender 2

(concealed) G448

Exhaust gas temperature
sender 3 for cylinder bank 1
G496

Heated catalyst
Flexible
pipe

Vorab-Grafik

Oxygen sensor 2
G108

Connection for differential pressure sender
G505

Heated catalyst 2

NOx sender
G295

Flexible pipe
Exhaust gas temperature
sender 2 for bank 2
G449

Catalytic converter
heater 2

Z120

Exhaust gas temperature
sender 3 for bank 2
G497

622_019

Reducing agent injector
N474

Mixer

Reducing agent injector N474 (metering valve) and mixer
The metering valve is an air-cooled solenoid valve, and its task is to
provide a continuous supply of reducing agent to the SCR-coated
diesel particulate filter. The reducing agent injector is activated by
the engine control unit in a pulse-width-modulated (PWM)
fashion. An even distribution of ammonia in the SCR-coated diesel
particulate filter is the key to a high degree of implementation.

16

The so-called mixer is located directly downstream of the reducing
agent injector and is responsible for optimally mixing the reducing
agent and exhaust gases. The mixer induces turbulence in the
exhaust gas stream and in the reducing agent; it also acts as an
evaporator, its hot surface causing some of the reducing agent to
change from a liquid to a gaseous state.

Rear section of exhaust system
In the further course of the exhaust system, both pipes merge into
a connecting pipe. The combined exhaust gas streams then flow
into the two main silencers.
The NOx sender 2 G687 is mounted on the connecting pipe
housing.

This sensor monitors the carbon monoxide (CO) produced during
the regeneration cycle and the small quantities of ammonia arising
from the high temperature gradients during regeneration of the
diesel particulate filter. Both values influence the quantity of
reducing agent injected.

Catalytic converter heater Z119 and Z120
The active heating plate provides a significant reduction in emissions both during the start phase and at low engine load. The
heating plate has a power output of 500 watts and is located
directly upstream of the main catalytic converter. In SCR systems,
the heated catalyst is able to optimally evaporate the injected
reducing agent and thereby increases the efficiency of the SCR
catalytic converter.
These heated metal catalytic converter not only increase the
operating temperature by up to 100 °C, but also allow NOx conversion to begin much earlier by injecting the reducing agent onto the
heated diesel particulate filter.
To keep the catalytic converter warm for as long as possible, the
heating plate and the catalytic converter are encased in an insulating layer and a second stainless steel housing.

Exhaust gas temperature sender 3
for cylinder bank 1
G496

Oxygen sensor
G39
Connection of catalytic
converter heater 1
Z119

Heating plate

SCR-coated diesel particulate filter

Exhaust gas temperature sender 2
G448

Oxidising catalytic converter
622_049

Exhaust gas temperature sender 4 for bank 1
G651

NOx sender 2
G687

Exhaust gas temperature sender 4 for bank 2
G649

Connecting pipe

622_004
17

Fuel and reducing agent tank
Reducing agent tank
An active fuel tank and, depending on model, an auxiliary passive
fuel tank serving as a reducing agent reservoir are used in addition
to the conventional diesel fuel tank.

The pressure relief valve has also been deleted with the integration
of the service vent into the diaphragm filler cap. Both tanks, if
available, are connected to the filler neck by ventilation lines.

Audi Q7
Two reducing agent reservoirs, an active tank and a passive tank,
have been added to the conventional diesel fuel tank.
The capacity of the diesel fuel tank has been kept at 100 litres by
making optimal use of available underbody design space.

The reducing agent storage capacity of approximately 23 litres is
distributed to the reducing agent active tank directly below the
filler neck (7.5 litres) and the underbody reducing agent passive
tank (15.5 litres). The diesel fuel tank is filled, as is customary, via
the tank filler neck. Both filler necks can be accessed via the tank
flap.

Overview
Transfer line
Reducing agent
filler neck

Reducing agent active tank (7.5 litres)

Bleeding/vent line
Reducing agent pump
V437

Diesel fuel tank (100 litres)

Reducing agent passive tank
(15.5 litres)

Bleeding line

Filling line

622_011

Reference
For more detailed information about the function of the reducing agent system in the Audi Q7, please refer to Self-Study
Programme 428 "Audi 3.0l V6 TDI engine with ultra low emission system (EU6, LEV II, BIN5)".
18


Reducing agent active tank
The reducing agent pump V437, the overflow connection for filling
the reducing agent passive tank, the connection for filling the
reducing agent passive tank, and the heated supply and return
lines are mounted on the reducing agent active tank.

The reducing agent active tank is heated and has built-in sensors.

When the active tank is filled, the reducing agent flows into the
reducing agent passive tank under gravity after the preset level in
the reducing agent active tank is reached.

View from below
Swirl pot

Overflow fitting

Supply line

Return line

Reducing agent pump
V437

Connection to
reducing agent injector
N474
Overflow

The reducing agent passive tank serves as additional storage
capacity, is not heated and does not have any built-in sensors. The
reducing agent transfer pump V436 which circulates the reducing
agent is mounted on it. The pump is configured as a diaphragm
piston pump and activated by the engine control unit by means of
analogue signals.
The transfer pump V436 is activated by the engine control unit
J623 and pumps the reducing agent from the reducing agent
passive tank into the reducing agent active tank. The reducing

agent transfer pump V436 is activated whenever the reducing
agent tank sender G684 in the reducing agent active tank detects a
low fill level, and provided that the vehicle is travelling faster than
10 kph.
The fuel tank sender may not be at its max. level for short times
due to sloshing movement of the reducing agent on winding roads.
The engine control unit J623 recognises this condition and likewise
activates the reducing agent transfer pump.

Connection to
passive tank

622_017

Reducing agent passive tank

Reducing agent
transfer pump
V436

622_018
19


Audi A6 ’11 and Audi A7 Sportback
A 17-litre reducing agent tank is used on the underbody in addition
to the fuel tank, which holds approx. 73 litres.
This reducing agent tank is configured as the active tank.

It is filled from the exterior via a filling line located adjacent to the

filler neck and is identified by a black filler cap. It is made from
high-grade plastic and adapted to the underbody contours by blow
moulding.

Overview
Diesel / reducing agent filler neck

Bleeding line

622_050

Diesel fuel tank

Filling line

622_010

Reducing agent active tank (17 litres)

20

Bleeding line


Reducing agent active tank
A compact swirlpot is now mounted on the reducing agent active
tank. This swirlpot accommodates the reducing agent pump and
built-in sensors for monitoring the reducing agent temperature,
reducing agent pressure and fill level, as well as the reducing
agent system heater.

The reducing agent metering system control unit J880, the connection for the metering line to the water-cooled reducing agent
injector, the drain outlet and the electrical connector are arranged
on the exterior of the swirlpot.

Overview

Filling line

Bleeding line

Swirlpot with reducing agent pump
V437

622_013

View from below

Reducing agent tank heater
Z102

Connection for heated metering line
to reducing agent injector
N474
Swirlpot with reducing
agent pump
V437
Reducing agent drain outlet
Reducing agent metering
system control unit

J880
622_013
21


Audi A4 ’14
Due to space constraints, active and passive reducing agent tanks
with a total capacity of 20 litres are used on this model in addition
to the fuel tank, which holds approx. 61 litres.
These reducing agent tanks are simultaneously filled from the
exterior via a split filling line located adjacent to the tank filler
neck.

The reducing agent filler neck is identified by a black filler cap.
Both reducing agent tanks are made from high-grade plastic (PEHD
= polyethylene) and optimally adapted to the available underbody
design space by means of blow moulding.

Overview
Reducing agent passive tank

Reducing agent
filler neck

Reducing agent transfer pump
V436

Diesel fuel tank

View from below

Reducing agent active tank

Swirlpot with reducing
agent pump
V437
Reducing agent metering
system control unit
J880

Heated metering line to
reducing agent injector
N474

622_007
22


Reducing agent active tank
The filling line connection, the bleeding and vent lines, the drain
outlet and the filling line of the transfer pump on the passive tank
are located on the exterior of the active reducing agent tank.
The reducing agent metering system control unit J880 and the
swirlpot are also mounted on it.

Transfer pump filling line

This swirlpot accommodates the reducing agent pump and built-in
sensors for monitoring the reducing agent temperature, reducing
agent pressure and fill level, as well as the reducing agent system

heater.
The connection for the heated metering line to the water-cooled
reducing agent injector and the electrical connector are arranged
on the exterior of the swirlpot.

Bleeding line (heated)
Filling line from filler
neck

Reducing agent
tank sender
G684

Reducing agent metering
system control unit
J880

Heated metering line to reducing
agent injector
N474

Swirlpot with reducing agent pump
V437

622_040

Reducing agent passive tank
The reducing agent passive tank serves as additional storage
capacity, is not heated and does not have any built-in sensors. The
reducing agent transfer pump V436 which circulates the reducing

agent is mounted on this tank. It is designed as a diaphragm
piston pump and activated by means of analogue signals. The
reducing agent transfer pump V436 is activated by the engine
control unit J623 via the reducing agent metering system control
unit J880.

The pump transfers reducing agent from the reducing agent
passive tank to the reducing agent active tank. The reducing agent
transfer pump V436 is activated whenever the reducing agent tank
sender G684 in the reducing agent active tank detects a low fill
level, and provided that the vehicle is travelling faster than 10 kph.

Bleeding line

Filling line

Transfer line to active tank

Reducing agent transfer pump
V436

622_041
23


Audi A8 ’10 and Audi A8 ’14
Due to space constraints, active and passive reducing agent tanks
with a total capacity of 27 litres are used on this model in addition
to the fuel tank, which holds approx. 90 litres.
Only the active reducing agent tank is filled from the exterior via

the filling line located adjacent to the tank filler neck; it is identified by a black filler cap on the A8 ’10 and by a blue filler cap on
the A8 ’14 and later models.

The reducing agent passive tank in the boot can be filled using
filling unit VAS 6542 or the filling bottle (Kruse bottle1)). The fuel
tank is made from high-grade plastic (PEHD = polyethylene) and
optimally adapted to the available underbody design space by
means of blow moulding.
Use VW and Audi approved reducing agent AdBlue® as specified by the VW
and DIN 70070 standards. Original part number: G 052 910 A2 for
0.5 gallon drum, G 052 910 A4 for 10-litre drum.

1)

Overview - Audi A8 ’14
Reducing agent
active tank
Reducing agent metering
system control unit
J880

Bleeding line

Transfer line

Reducing agent
transfer pump
V436

Reducing agent

passive tank
(on Audi A8 ’14 only)

Reducing agent
filler neck

Filling line

Swirlpot with reducing agent pump
V437

Heated metering line to reducing
agent injector
N474

Diesel fuel tank

622_009

24


Reducing agent active tank on Audi A8 ’10
This reducing agent tank is configured as the active tank. It has a
capacity of 20 litres and is mounted on the rear right side wall in
the boot. It is directly filled from the exterior.

The swirlpot, including all sensors, the reducing agent pump, the
reducing agent heater and the reducing agent metering system
control unit, is located on the reducing agent tank.

Bleeding line connection

Filling line connection
Heated metering line to reducing
agent injector
N474

Reducing agent tank heater
Z102

Swirlpot with reducing
agent pump
V437

Reducing agent tank sender
G684
622_042

Reducing agent active tank on Audi A8 ’14
Due to space-saving constraints, a reducing agent active tank with
a reduced capacity of 16 litres is installed in the boot on the rear
right. To ensure an adequate supply of reducing agent in between
service visits, the reducing agent metering system has an additional 12-litre passive tank.

In this case also, the reducing agent active tank is filled from the
exterior via the filler neck. The tank accommodates the swirlpot
including sensors, the reducing agent pump, the reducing agent
heater and the reducing agent metering system control unit. The
active tank is filled from the passive tank via a transfer line.

Filling line connection
Reducing agent metering system
control unit
J880
Connection for bleeding line
reducing agent filler neck

Connection for transfer line from
transfer pump on passive tank

Connection for bleeding line
from passive tank
Heated metering line to reducing
agent injector
N474

Swirlpot with reducing agent pump
V437
Reducing agent tank heater
Z102

622_026
25