10” or 11” single diaphragm brake servos are used on all
left hand drive A3 models. The size is dependent on engine
type. The brake servo is newly developed and is considerably lighter than the predecessor. The weight reduction was
achieved by using high tensile steel for the outer shells and
revised contours.
Brake pressure build-up is based on a single rate characteristic.

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The pedal assembly of the 2015 A3 is a new design.
The brake and accelerator pedals are suspended from a
common plastic bearing pedestal. This was done to
reduce weight.
Plastic bearing pedestal

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Electro-mechanical parking brake
(EPB)
An electro-mechanical parking brake system is used on the
A3 model line for the first time. The system and software
is supplied by Continental.

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15

Design and function
Left and Right Parking Brake Motors V282 and V283 are
different from the TRW components used in previous Audi
models. Gear reduction is provided by a two-step worm
drive assembly. The required self-locking effect is produced
in the second step.
The brake caliper spindle is inserted into the spur gear of
the second gear step when assembling the parking brake
motor. The spindle and spur gear are connected by internal
and external Torx® profiles. The spindle is a component
part of the ball screw and is mounted in the brake caliper.
It applies pressure to the inner face of the brake piston via
the spindle nut.

The brake and release operations are controlled in the
same way as in the EPB systems used in other Audi models.
Deactivation of the maximum clamping force of approximately 17.5 kN is controlled by applying up to approximately 12A of electrical current. A temperature model in
the ABS/ESP Control Module calculates the cooling of the
brake discs and pads when the vehicle is parked and, if
necessary, tightens the parking brake up to three times by
briefly activating the electric motors.
Brake caliper spindle
engagement

The spur gear, driven by the electric motor, transmits the
rotational movement to the spindle. The thrust element
moves lengthwise when the spindle rotates. Depending on
the direction of rotation, the thrust element moves
towards the base of the brake piston or in the opposite
direction. As a result, the brake piston is pressed against
the brake pad (braking position) or moved away by the
brake pad (release position).

Worm gear
assembly of
second gear step
Worm gear
assembly of first
gear step

Electric motor

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Brake piston

Brake piston in
release position

Brake disc

Thrust piece
(spindle nut)

Ball screw

Spur gear of second
gear step

Spindle

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Brake pad

Brake piston in
applied position

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16

Service operations
The thickness of the outer brake pads on all wheels can also
be checked using measuring pin T40139A.

A brake pad wear indicator is installed on the right wheel
brake of the front axle on the 2015 A3. The contact is
attached to the inner brake pad.

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Brake pad

Measuring pin

The control software for the EPB is integrated in the
ABS/ESP Control Module. The service functions of the EPB
are accessed through Address Word 03. The Address Word
normally used for EPB (053) is unassigned.
To replace the rear brake pads, you must initiate the corresponding Test Plan using the VAS Scan Tool. The parking
brake is then opened as far as possible so that the brake
pads can be replaced. After replacing the brake pads, the
parking brake is closed and the required clearance between
the brake pad and brake disc is set automatically.
When installing the new brake pads, care must be taken to
ensure that the locking pins on the back plates engage the
brake piston pockets.

!
17

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Warning
Due to the modified design of the EPB parking brake motors, the self-locking effect is no longer provided by the spindle in
the brake caliper, but rather by the second gear step in the parking brake motor. As a consequence, the parking brake is
released as soon as the parking brake motor is detached from the brake caliper. To prevent the vehicle from rolling away
during service, it is important that the vehicle is be secured before disassembling the parking brake motors. The parking
brake motors should only be removed on a level surface with the remaining wheels blocked or on a vehicle lift.

ESP overview
The Continental ESP MK 100 system is used in the Audi A3.
This ESP system is a more advanced version of the ESP MK
60 system used in the predecessor model, both in terms of
its hardware and software. The ESP unit is mounted on the
right side long member in the engine compartment.

System components

ABS/ESP Control
Module J104

Hydraulic unit

ABS/ESP Control Module J104
Rotation Rate Sensor G202, Transverse Acceleration Sensor
G200 and Longitudinal Acceleration Sensor G251 have
been integrated with ABS/ESP Control Module J104. This
eliminates the use of ESP Sensor Unit G419 found in the
predecessor model.
The control software for the EPB has been integrated in
ABS/ESP Control Module J104. The control module
performance has been enhanced by using new electronic
components and more advanced software. The ABS/ESP
communicates via the Suspension CAN bus.

Hydraulic unit
Two versions of the hydraulic unit are used dependent on
the installation of Adaptive cruise control (ACC).
A hydraulic unit with special noise reduction features and
a reinforced pump are used on vehicles with ACC.

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Continental ESP MK 100

18

ABS Wheel Speed Sensors G44 - G47
Active wheel speed sensors are used on the 2015 Audi A3.
There are two configurations for the sensors at the rear
axle. If the vehicle is equipped with Audi park assist and/or
ACC, the sensors will additionally record the direction of
rotation of the wheels and the clearance between the
sensor wheel and sensor.

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System functions
The 2015 A3 has the same ESP system functions as its
predecessor model.

Another new feature is the post collision brake assist
function.

An additional new feature is the active brake pressure
build-up for the ACC function and Audi pre-sense front
brake operations.

This function reduces the danger of skidding and further
collisions during an accident by automatically initiating a
vehicle braking operation. The function is active during
head-on, side and rear collisions if a predetermined
deployment threshold is exceeded. If the threshold is
exceeded, the Airbag Control Module instructs the
ABS/ESP Control Module to brake the vehicle via a bus
message. The ABS/ESP system then builds up brake
pressure at all four wheels.

If the system identifies a situation of impending vehicle
instability based on the relevant signals, the brake system
is pre-filled. A moderate build-up of brake pressure is
initiated by the activation of the ESP pump. The purpose is
to eliminate the brake pad / disc clearance which reduces
the reaction time during subsequent braking manoeuvres.
The brakes are also pre-filled if an emergency braking
operation is initiated by the driver. During an emergency
braking maneouver, drivers usually take their foot of the
accelerator pedal very quickly and apply full braking. The
movement of the accelerator pedal is evaluated in these
situations.
The Hill Start Assist function is optional with the A3 for the
first time in this model series.

There are several conditions for activation. First, the
vehicle must be travelling at a speed greater than 6.2 mph
(10 kph). Further, the ESP system, hydraulic brake system,
and the on-board power supply must all remain intact
during the collision.
Automatic braking is deactivated during the following
driver actions:

•
•

The driver depresses the accelerator pedal.
The driver brakes by applying a brake pressure higher than the
brake pressure applied by the system.

If an ESP system fault has occurred, the post collision brake
assist function will not be available.

Reference
The actions implemented by the ABS/ESP Control Module for Audi pre-sense and pre-sense front are described in eSelf-Study
Program 990143, The 2015 Audi A3 Introduction.

Operation and driver information
If the ESP button on the instrument panel is pressed for
less than three seconds, Sport mode is activated. The TCS
function is simultaneously deactivated. Stabilizing ESP
inputs are not made until much higher wheel slip values.
If the ESP button is pressed for longer than three seconds,
TCS and ESP are both deactivated.

19

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Service operations
The ABS Control Module and hydraulic unit can be separated for repair. The same condition applies here as to the
predecessor model: control modules can be replaced individually but the entire ABS/ESP unit must be replaced if
hydraulic units are faulty.
After replacing an ABS/ESP Control Module, it must be
encoded online. Steering Angle Sensor G85 must be
calibrated and initialized through Power Steering
Control Module J500.

Since the control software for the electro-mechanical
parking brake is a function of ABS/ESP Control Module
J104, a function check is performed on the EPB by twice
opening and closing the parking brake. The ESP intake and
isolating valves are subsequently calibrated, as previously
in the predecessor model equipped with MK 60 EC.
The TPMS is also enabled at this time. The concluding
actuator diagnostics ensure that the hydraulic lines are
correctly connected to the hydraulic unit and the ESP
system is tested for proper function.

Several basic settings must then be configured. At the
same time, the brake pressure, longitudinal acceleration,
transverse acceleration and yaw rate senders are calibrated.

Special tool
VAS 6613

Wrist band
ESD table mat
with equipotential
bonding

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!

Note

To avoid damaging electronic components by electrostatic discharge, the control module and hydraulic unit
must always be removed/assembled using Special tool VAS 6613.

20

Steering system
Overview
The steering system concept for the 2015 A3 has been
adopted from the predecessor model. This includes the
electro-mechanical steering system and, a mechanically
adjustable steering column.

A progressive steering system will be offered as an option
in combination with the sports suspension at a later date.

Various steering wheels are used based on
vehicle options

Mechanically adjustable safety steering
column with stepless adjustment
2.3 in (60 mm) longitudinally
1.9 in (50 mm) vertically

Electro-mechanical steering with
Servotronic function is standard equipment

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Electro-mechanical steering
Design and function
The functional principle of the steering system has been
adopted unchanged from the predecessor model. Torque
assistance is provided by a second steering pinion which is
driven by an electric motor. A torque sensor determines
the steering torque applied by the driver. The electronic
control module determines the required torque assistance
in dependence on steering torque, vehicle speed, steering
angle, steering speed and other input variables. A major
modification compared to the predecessor model is the
use of a synchronous motor in place of an asynchronous
motor. By making this modification and by redesigning
the geometry of the steering housing, the overall weight
of the steering unit has been reduced by approximately
5.5 lb (2.5 kg).

The position of the electric motor's rotor is identified by a
rotor speed sender built into the motor. This sender has
the same functional principle as the sender used in the
predecessor model. A temperature sensor integrated in
the control module measures the output stage
temperature. If a predetermined limit is exceeded, power
steering assistance is incrementally reduced. If a system
fault is detected, power steering assistance is deactivated.
System faults are indicated to the driver visually by a
yellow or red indicator lamp and audibly by acoustic
signals.

Reference
For detailed information on the design and function of the electro-mechanical steering system, refer to eSelf-Study Program
993503, The 2006 Audi A3 Running Gear.
21

EPS pinion

Steering Motor Speed Sensor
G577

Steering angle sensor G85
Steering torque sensor G269

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Synchronous
Electro-mechanical Power
Steering Motor V187

Power Steering
Control Module
J500

Steering pinion

Progressive steering
(not available at model introduction)

Progressive steering is provided by a variable steering ratio.
A special rack gearing geometry is used to ensure that the
steering ratio is variable as a function of steering angle. A
progressive steering system will be offered as an option in
combination with the sports suspension at a later date.

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Rack

Steering pinion

Steering ratio

The steering ratio is at its highest when driving in a straight
line and during minor steering inputs near the center
position. The immediate vehicle response to steering inputs
conveys a sporty and direct steering feel to the driver.
At medium steering angles (for example, when driving on
winding country roads), the ratio is still large enough to
create a dynamic steering feel and reduce the need for
drivers to move their hands on the steering wheel.
Steering angle
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At large steering angles (for example, in inner-city areas or
when parking), the steering ratio is reduced to minimize
steering effort for the driver.

22

Service/diagnostic operations
The electro-mechanical steering system components
described here have self-diagnostic capability.

1. Special system status indication
Yellow warning lamp active:
The yellow warning lamp is activated in the following cases:

•

•

The end stops have not been programmed or Steering
Angle Sensor G85 is not calibrated. In this case, the fault
is registered and power steering assistance is reduced to
approximately 60%. Calibrating the steering angle
sensor deactivates the warning lamp again and automatically clears the DTC from the fault memory.

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A system malfunction has occurred: in these cases, an
additional text message appears in the DIS and the fault
is registered. The vehicle can be driven to the nearest
repair center, but with reduced steering assistance.

Red warning lamp active:
The red warning lamp is activated in the following cases:

•

•

A system test is run internally directly after switching
the ignition ON, during which the warning lamp is briefly
activated for test purposes. If the system is fault-free,
the warning lamp goes out again after a few seconds. In
vehicles with the optional advanced key, the yellow
warning lamp for testing the electrical steering lock
system is briefly activated before the red warning lamp.

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If the warning lamp is continuously lit, it means that a
system fault has been detected. In these cases, an additional text message appears in the DIS and the fault is
registered. It is no longer possible to continue driving.

2. Removing, installing and
replacing system components and
follow-up work
There is no provision for the replacement of individual
components. In the event of a fault, the complete steering
unit must always be replaced.
After installation, Steering Angle Sensor G85 must be
calibrated before Power Steering Control Module J500 is
encoded. The steering end stops are also stored during
this calibration procedure.
The power steering map required for the vehicle is activated
after the calibration is made. The characteristic maps are
selected depending on front axle load and vehicle weight.

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Power steering