differential SAAB 9-3 2009 Owners Manual

173 Starting and driving
All-wheel drive (XWD)3Essentially, the system consists of a PTU
(Power Take off Unit), propeller shaft, RDM
(Rear Drive Module which contains an elec-
tronically controlled plate clutch, final drive
gear and differential) and driveshafts. This
system enhances driving characteristics
and stability. The system is always active
and cannot be deactivated. It works
together with the ESP system and the
engine and transmission control modules.
When driving at a constant speed, approx.
95% of the torque is distributed to the front
wheels and approx. 5% to the rear wheels.
The torque is distributed steplessly and
instantaneously between the front and rear
wheels, depending on the driving condi-
tions. If the car is fitted with eLSD (electron-
ically controlled plate clutch between the
rear wheels), the torque can also be distrib-
uted individually to the relevant rear wheel.For optimum system function, the car’s tires
should not have varying degrees of wear.
When the XWD system requires service,
the following message is shown on the SID:
When the service message is displayed,
the XWD system may have limited func-
tionality (or be completely disabled in
some cases, i.e. the car switches to
front-wheel drive). Contact a workshop
for information. We recommend that you
contact an authorised Saab dealer.
Traction Control
System (TCS)Anti-spin systemHow the system worksThe Traction Control System (TCS) is
designed to prevent wheelspin. This
enables the car to achieve the best possible
grip and, hence, maximum tractive effort,
together with greater stability.
The TCS system uses information from the
ABS system’s wheel speed sensors to
determine whether any wheel is spinning. If
any wheel is spinning, this is reduced on
all-wheel drive cars initially by changing the
torque distribution, secondly by reducing
the engine torque, and thirdly with the aid of
the wheel brakes. On front-wheel drive cars,
wheelspin is reduced initially by reducing
the engine torque, and secondly with the aid
of the wheel brakes. Service XWD.
WARNING
When driving normally, the TCS system
helps to improve the car’s stability, and
driveability under slippery road and
extreme driving conditions. The TCS
must not be regarded as a system to
enable the driver to maintain higher
speeds. The same precautions must be
adopted as normal for safe cornering and
driving on slippery roads.
93_US_MY09.book Page 173 Tuesday, April 15, 2008 10:30 AM
ProCarManuals.com