Coolant thermostat
After-Run Coolant
Pump V51

Engine oil cooler 2
(water to oil)
Coolant thermostat
for engine oil cooler

Flow restrictor

Coolant return from the
cooling duct plate

Coolant supply to
cooling duct plate

642_013

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Function diagram

Chassis CAN high

J492

Chassis CAN low

Key:
Ground cable

G943

Positive cable
Signal wire
G942
G942
G943
J492
V181

All Wheel Drive Hydraulic Pressure Sensor
All Wheel Drive Hydraulic Temperature Sensor
All Wheel Drive Control Module
Haldex Clutch Pump

V181
642_014

All Wheel Drive Control Module J492
J492 is located behind the luggage compartment tray
adjacent to the vehicle battery.

Diagnosis:

A different control module version is required for each
engine version. Its software is adapted at the factory on the
basis of engine power parameters. The control module and
the programming values are assigned to the vehicle based
on the vehicle identification number. When the control
module is replaced, it is important to follow the instructions given by the VAS Scan Tool Test Plan. The Test Plan
includes all steps to be performed.

›› The electrical wiring is checked for open circuit as well as
for short circuit to ground and positive.
›› Data exchange across the CAN bus is monitored.
›› The parameters for adaptation to engine power output
are checked.
›› The VIN can be checked for plausibility. If the All Wheel
Drive Control Module or Vehicle Electrical System Control
Module are switched between vehicles for diagnostic
purposes and not programmed, a DTC will be registered.
›› The main processor of the control module is diagnosed.
›› The temperature of the control module is monitored.
›› The wheel speed signals are checked for plausibility. If
the driver adopts a highly dynamic driving style, it can
trigger a sporadic DTC when on wet or icy road surfaces
that afford very little friction.
›› The all-wheel drive clutch function is checked for plausibility. If the Haldex Clutch Pump V181 is activated, a
pressure must be measurable inside the pressure
chamber and torque must be transmitted.

642_020

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›› The temperature of the clutch plates is calculated based
on the measurement of All Wheel Drive Hydraulic Temperature Sensor G943. If a default value is exceeded as a
result of high power demand, a message is displayed in
the instrument cluster and, in accordance with a limphome concept, the all-wheel drive clutch is not activated
until the Haldex oil has cooled down.

Sensors and actuators
The pressure and temperature sensors of the Haldex unit
allow highly precise control while extending the diagnostic
options and improving component protection.

All-wheel drive clutch

All Wheel Drive Hydraulic
Pressure Sensor G942
G942 measures the hydraulic pressure in the pressure
chamber of the clutch piston. The measured value is used
to control the clutch and to help determine the deterioration of the oil. The measured value also helps protect the
Haldex Clutch Pump V181 from running dry. If no pressure
is measurable when V181 is activated, DTC is registered
and the pump stops running. A corresponding message is
displayed in the instrument cluster. The pumping capacity
of the pump must be checked after repairs are made.

G942

If the hydraulic pressure sensor is replaced, the offset value
stored in J492 for the old pressure sensor must be deleted
using the Basic Settings function of the VAS Scan Tool.
Pressure chamber

Diagnosis:
›› The electrical wiring is checked for open circuit as well as
for short circuit to ground and positive.
›› Plausibility criterion: When the Haldex Clutch Pump
V181 is activated, a pressure must be measurable inside
the pressure chamber.

G943
642_021

Substitute signal:
›› There is no substitute signal, refer to "Limp-home
concept" on page 26.

All Wheel Drive Hydraulic
Temperature Sensor G943
G943 measures the temperature of the Haldex oil in the
sump of the mechanical powered pump. The measured
value is used to determine the deterioration of the oil and
helps prevent the clutch from overheating.
Diagnosis:
›› The electrical wiring is checked for open circuit as well as
for short circuit to ground and positive.
›› Plausibility criterion: if the temperature of the Haldex oil
exceeds the limit, the all-wheel drive clutch is not activated further.
Substitute signal:
›› There is no substitute signal, refer to “Limp-home
concept” on page 26.
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Haldex Clutch Pump V181
V181 produces hydraulic pressure in the all-wheel drive
clutch. Refer to page 16. The wiring harness for V181
also houses the wiring for G492 and G493.
Diagnosis:
›› The electrical wiring is checked for open circuit as well as
for short circuit to ground and positive.
›› Plausibility criterion: when V181 is activated, a pressure
must be measurable inside the pressure chamber.
Output check: refer to page 25.
›› "All-wheel drive clutch function test"
›› "Ventilation and hydraulic leak test"
Checking the pumping capacity of the pump:
›› Is the sump for Haldex Clutch Pump V181 filled?
Refer to notes on page 13
›› Perform "all-wheel drive clutch function test".
›› Perform "ventilation and hydraulic leak test" and check
final drive for leaks (visual inspection).

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Haldex Clutch Pump V181 with
wiring for G942 and G943
642_022

Audi drive select
The driver can use the Audi drive select button to select
between the "comfort", "auto", "dynamic" and "individual"
modes. These modes influence the all-wheel drive control
setup with respect to the distribution of drive power
between the front and rear axles.
The Performance button sets the "performance" mode and
selects the last active setup (last mode), that is, snow, wet
or dry. Setups can be selected using the adjustment ring. In
snow, wet and dry modes the pre-control values for road
surface friction are set to within narrower bounds. The
all-wheel drive control module, which continuously measures the friction coefficients of the road surface, is able to
react more quickly and with greater precision thanks to
more specific pre-control values. This improves vehicle
handling on dry, wet and snow-covered roads and provides
more sporty driving dynamics.

All-wheel drive control setups available using Audi drive
select

Audi drive select button

Comfort
In Comfort mode the distribution of drive power is front
axle-orientated. Cornering behavior is neutral tending to
slight understeer at the limits of dynamic performance.
Auto
In Auto mode drive power is evenly distributed between the
front and rear axles. Handling is neutral during cornering.
Dynamic
In Dynamic mode the distribution of drive power is rear-orientated. Handling is more sporty and cornering behavior is
neutral tending to slight oversteer at the limits of dynamic
performance.

Performance button with
adjusting ring for selecting the
snow, wet and dry modes

642_025

Individual
In Individual mode the driver can choose transmission and
all-wheel drive setups independently of other vehicle
systems.
Performance
In Performance mode drive power is evenly distributed
between the front and rear axles, as is the case in “auto”
mode.

!

Note
Activating the Performance mode limits the range of the ESC and TCS stabilization functions. Only activate Performance
mode if you have the necessary driving skills and the traffic conditions permit.

Reference
For further information about Audi drive select and how the performance of the Audi R8, refer to the Owner's Manual.

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Operating situations
Certain operating situations affect all-wheel drive control.
The main operating situations are set out below and
explained in the following table.

Launch control program
The Launch Control Program enables and regulates the
maximum acceleration of the vehicle from a standing start.
The all-wheel drive clutch delivers the maximum possible
amount of torque for the front axle. Refer to the Owner's
Manual for operating instructions and other information.

Torque vectoring
Torque vectoring is a software function of the ESC control
module. During cornering at high speeds, the ESC control
module determines the reduced load on the wheels on the
inside of the curve and the increased load on the wheels on
the outside of the curve.
Controlled braking intervention builds up stabilizing torque
at the wheels under increased load on the outside of the
curve, allowing more drive power to be transmitted from
the wheels under reduced load on the outside of the curve.
In addition to providing a dynamic axle load distribution,
torque vectoring affects the maximum amount of drive
power which can be transmitted by the front axle and
therefore is incorporated into the all-wheel drive control
process.

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This table summarizes the torque requirements and the
states of the all-wheel drive clutch for each of the listed
operating situations.

Operating situations

Required front axle
torque

State of
all-wheel drive clutch

Speed differential
between front and
rear axles

Acceleration,
kickdown, Launch
Control Program

high

up to maximum torque /
maximum pressure

low because clutch is closed to
maximize traction

Fast driving

depending on driving situation

depending on
driving situation

dynamic driving style: low
because the clutch is closed
conservative driving style:
medium, resulting primarily
from the axle ratios

Driving on a slippery
surface

depending on driving situation

depending on
driving situation

depending on driving situation, tending to low to achieve
good traction

Parking

low

low contact pressure

low, defined by the design and
dependent on the curve radii
of the front and rear axles

Braking

0 Nm

open

All-wheel drive clutch open,
differential speed is not influenced by the all-wheel drive

Stopping

depending on driving situation

depending on
driving situation

when the vehicle is stationary,
the clutch is proactively
closed.
if a subsequent acceleration
phase is predicted.

Downhill assist

depending on driving situation

depending on
driving situation

Hill Start Assist

depending on driving situation

depending on
driving situation

Towing

0 Nm

open if the engine is not
running and no gear is
selected **

low because vehicle is only
allowed to be towed on 4
wheels

**Before towing the vehicle, the parking lock emergency release mechanism
must be activated.
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Service
Using the VAS Scan Tool
All Wheel Drive Control Module J492 is accessed with the
VAS Scan Tool using Address Word 22.
The following Guided Functions can be performed:
›› Control unit identification
›› Read measured data
›› Basic setting
›› Reset to factory settings of control unit manufacturer:
This function deletes all programmed values. The
control module must be re-initiated.
Advantage: with this function, control module can be
interchanged between vehicles.
›› Reset programmed values for oil deterioration:
If the Haldex oil is changed in the course of routine
servicing, the programmed values for oil deterioration
must be reset.
›› Reset the offsets of G492:
If the hydraulic pressure sensor is replaced, the offset
value must be reset.
›› Actuator diagnostics (Output checks)
›› All-wheel drive clutch function test:
If the function is active, the all-wheel drive clutch is
closed up to a speed of 6.2 mph (10 km/h). Driving the
vehicle with the all-wheel drive clutch closed noticeably
increases the strain on the driveline at medium steering lock. The vehicle begins to shudder. When the
vehicle reaches a speed of 6.2 mph (10 km/h), the
all-wheel drive clutch opens and a jolt is noticeable
when the driveline is relieved of load. The jolt which
occurs when the driveline is relieved of load is a general
indication that the all-wheel drive is functioning.
›› Ventilation and hydraulic leak test.
This function allows the Haldex Clutch Pump V181 to
build up a pressure of over 638 psi (44 bar) and vents
the air in the pressure chamber via the pressure relief
valve. Pump operation is clearly audible because the
pump runs at maximum load during the ventilation
phase.

25

›› Replace control module
›› The programmed values from the old control module
are read out. If the old control module can no longer
be accessed, the programmed values for oil deterioration and pressure sensor offset cannot be read out
and transmitted. In this case, the Haldex oil must be
changed.
›› The control module to be initialized reads in the
vehicle identification number via the Chassis CAN
after the first terminal change and is assigned to the
vehicle.
›› The basic software of the new control module is
supplied with the performance-specific parameters.
›› The programmed values of the old control module are
transferred.
›› Changing high-performance oil for Haldex clutch
The programmed values for oil deterioration are reset.
›› Check SVM control module configuration
The validity of the software and the performance-specific
parameters are checked and adapted to suit the vehicle.

Maintenance and change intervals
The Haldex oil and the axle oil currently have a servicing and
change interval of approximately 110,000 m (180,000 km)
or 10 ten years.
Refer to the instructions given in ElsaPro. The bottom edge
of the Haldex oil filler plug thread is not a check mark. If
the Haldex oil is changed, the quantity of oil specified in
ElsaPro must be observed.

Reset the programmed values for oil deterioration (aging)
in the all-wheel drive control module using the “changing
high-performance oil for Haldex clutch” function of the VAS
Scan Tool.
Note: mixing up the two oil supplies will cause irreparable
component damage.

Towing
Flat bed towing is always preferred when transporting a
disabled R8.
If this is not possible, the vehicle may only be towed with
both axles on the ground. Towing the vehicle with a raised
front axle will damage the front final drive and is not permitted. The maximum towing distance is approximately
30m (50 km). The maximum towing speed is approximately
30 mph (50 km/h).

Warning lights
If the yellow warning light appears in the instrument
cluster, it is normally possible to continue driving the
vehicle. Information is displayed informing the driver of
what to do.

642_023

If the red warning light appears in the instrument cluster,
the driver is instructed not to drive any further.

642_024

Limp-home concept
The all-wheel drive system initiates different limp-home
programs depending on the nature of the fault.
›› If certain signals cannot be registered, the driving
dynamics control system may not be fully functional. In
this case the all-wheel drive clutch is only activated to a
limited degree in order to improve traction.

›› If a defined temperature value is exceeded under very
high power demand, the all-wheel drive system is no
longer activated.
In all cases, warnings are displayed in the instrument
cluster.

›› In the event of serious faults, the all-wheel drive system
is deactivated.

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Knowledge assessment
An On-Line Knowledge Assessment (exam) is Available for this eSelf-Study Program.
The Knowledge Assessment is required for Certification credit.
You can find this Knowledge Assessment at:
www.accessaudi.com
From the accessaudi.com Homepage:
›› Click on the “ACADEMY” tab
›› Click on the “Academy site” link
›› Click on the Course Catalog Search and select “950163 - Front final drive 0D4”
Please submit any questions or inquiries via the Academy CRC Online Support Form
which is located under the “Support” tab or the “Contact Us” tab of the Academy CRC.

Thank you for reading this eSelf-Study Program and taking the assessment.

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950163
All rights reserved.
Technical specifications are
subject to change without notice.
Audi of America, LLC
2200 Ferdinand Porsche Drive
Herndon, VA 20171
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