2002-2010 Porsche Cayenne SUV Driving and Driving Safety -> Power-transmission and running-gear control systems User Manual
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Driving and Driving Safety -> Power-transmission and running-gear control systems for Your Porsche Cayenne SUV First Generation (2002-2010)

190 Driving and Driving Safety
Power-transmission and running-gear control systems
A complex network of all control systems acting in power transmission and in the running gear has been realised in your Porsche.
All control systems are networked with the aim of combining the best possible driving performance with maximum safety.
The following systems are involved:
System/designation Scope
PTM
Porsche Traction Management
– Full-time all-wheel drive
– Electronically controlled centre differential lock
– Automatic brake differential (ABD)
– Traction control system (TCS)
– Reduction gear/Low Range
PTM Plus
Porsche Traction Management
In addition to the PTM features, PTM Plus also includes:
– Electronically controlled rear differential lock
PSM
Porsche Stability Management
– Stability management system
– Anti-lock brake system (ABS)
– Brake system prefilling
– Brake booster
– Traction control system (TCS)
– Automatic brake differential (ABD)
– Engine drag torque control (MSR)
Air suspension
with level control and height adjustment
– Full load bearing air spring struts with integral shock absorbers
– Air supply system with pressure accumulator
PASM
Porsche Active Suspension Management
– Shock absorber system with adaptive, continuous shock absorber control
PDCC
Porsche Dynamic Chassis Control
– Active chassis control system to stabilise roll tendency of vehicle body when driving
Driving and Driving Safety 191
Porsche Traction Management (PTM)
Porsche Traction Management is a full-time all-
wheel control system designed to influence the
longitudinal and lateral dynamics. It is closely
linked with the Porsche Stability Management
(PSM) control system.
PTM ensures the best possible power distribution
to the four driven wheels at the front and rear
axles. The system realises this optimal traction by
intervening in the lock control function of the
transfer box and rear differential. PTM is active at
all times and, unlike PSM, cannot be switched off.
Advantages of PTM
– Obvious improvement in traction, driving
stability and steering ability of the vehicle.
– Vehicle is more manageable when driven at its
performance limits.
– Improved straight-ahead tracking and stability.
– The above features allow for a sportier setup
of the running gear.
– TCS and ABD further enhance traction for all
wheels.
Safety notes!
In spite of the advantages of PTM, it is still the
driver’s responsibility to adapt his driving style and
manoeuvres in line with road and weather condi-
tions, as well as the traffic situation.
The increased safety that is provided should not
induce you to take greater risks with your safety.
The limits set by the physics of driving cannot be
overcome, even with PTM.
Risks of accident due to inappropriate speed
cannot be reduced by PTM.
Full-time all-wheel drive
With the four-wheel drive, the drive power is
variably distributed to the front and rear wheels.
Power distribution and wheel speed compensation
between the front and rear axles is realised with a
transfer box.
Distribution of the drive power depends on the
wheel speed difference between the two axles.
The transfer box always controls power distribu-
tion in such a way that optimal propulsion is
achieved, even on an unfavourable road surface.
Full-time all-wheel drive ensures optimum handling
and a high level of driving stability.
Safety notes!
In spite of the advantages of four-wheel drive, it is
still the driver’s responsibility to adapt his driving
style and manoeuvres in line with road and
weather conditions, as well as the traffic situation.
The increased safety that is provided should not
induce you to take greater risks with your safety.
The limits set by the physics of driving cannot be
overcome, even with four-wheel drive.
Risks of accident due to inappropriate speed
cannot be reduced by four-wheel drive.
192 Driving and Driving Safety
Automatic brake differential (ABD)
The ABD system controls the front and rear axles
separately. If one wheel of an axle starts to spin,
it is braked so that the other wheel on the same
axle can be driven.
ABD recognises different driving states, and it
features control strategies adapted to these
states. In situations in which little propulsive power
is required, such as when the vehicle moves off on
a level gravel surface, traction control already
becomes active at low engine speeds. If a large
amount of propulsive power is required, such as
when moving off on an uphill slope or for rapid
acceleration, the ABD system is adapted accord-
ingly.
A special off-road driving programme is used in
Low Range mode.
Traction control system (TCS)
The traction control system prevents the wheels
from spinning by adjusting the engine power,
thereby ensuring good lane-holding ability and
stable handling.
Porsche Stability Management (PSM)
PSM is an active control system for stabilisation of
the vehicle during extreme driving manoeuvres. It
is networked with the Porsche Traction Manage-
ment (PTM) system.
PSM makes use of both the ABD and TCS
systems, as well as the known functions of the
anti-lock brake system (ABS) and engine drag
torque control system (MSR).
Safety notes!
In spite of the advantages of PSM, it is still the
driver’s responsibility to adapt his driving style and
manoeuvres in line with road and weather condi-
tions, as well as the traffic situation.
The increased safety that is provided should not
induce you to take greater risks with your safety.
The limits set by the physics of driving cannot be
overcome, even with PSM.
Risks of accident due to inappropriate speed
cannot be reduced by PSM.
Advantages of PSM
– Best possible traction and lane-holding ability
in all driving situations – even on road surfaces
with varying friction.
– The system compensates for undesired
vehicle reactions (Ferraria effect) when the
driver releases the accelerator pedal or brakes
on bends. This compensation functions up to
the maximum lateral acceleration.
– PSM actively stabilises the vehicle as required
during dynamic driving manoeuvres (e.g. rapid
steering movements, during lane changes or
on alternating bends).
– Improved braking stability on bends and on
different or varying road surfaces.
– Improved brake functioning and reduced
stopping distance in the event of emergency
braking.
Driving and Driving Safety 193
Readiness for operation
PSM is switched on automatically every time you
start the engine.
Function
Sensors at the wheels, brakes, steering system
and engine continuously measure:
– Speed
– Direction of travel (steering angle)
– Lateral acceleration
– Longitudinal acceleration
– Rate of turn about the vertical axis
PSM uses these values to determine the direction
of travel desired by the driver.
PSM intervenes and corrects the course if the
actual direction of motion deviates from the
desired course (steering-wheel position):
It brakes individual wheels as needed. If neces-
sary, PSM additionally influences the engine power
or the gear-changing characteristic of Tiptronic in
order to stabilise the vehicle.
The events below inform the driver of PSM control
operations and warn him to adapt his driving style
to the road conditions:
– The multi-functional information light on the
instrument panel flashes.
– Light in the PSM Off button flashes.
– Hydraulic noises can be heard.
– The vehicle decelerates and steering-wheel
forces are altered as PSM controls the brakes.
– Reduced engine power.
– The brake pedal vibrates and its position is
changed during braking.
In order to achieve full vehicle deceleration,
foot pressure must be increased after the
brake pedal has begun vibrating.
Examples of PSM control operations
– If the front wheels of the vehicle drift on a
bend, the engine power is reduced and the
rear wheel on the inside of the bend is braked
if necessary.
– If the rear of the vehicle swings out on a bend,
the front wheel on the outside of the bend is
braked.
– Brake system prefilling:
The brake system is prepared for possible
subsequent emergency braking if the acceler-
ator pedal is released suddenly and quickly.
The brake system is prefilled and the brake
pads are already applied gently to the brake
discs.
– Brake booster:
In the event of an emergency braking operation
where the pedal force is insufficient, a brake
booster provides the braking pressure neces-
sary for maximum deceleration at all 4 wheels.
Combined operation of PSM and PTM/PTM
Plus
In order to ensure optimum stabilisation of the
vehicle, the centre differential lock (PTM) and
where appropriate also the rear differential lock
(PTM Plus) are also opened when PSM interven-
tions occur.
Tip on driving
When PSM is switched off, wheel-specific brake
interventions and the traction control system
(TCS) are also inactive.
The automatic brake differential (ABD) remains on.
194 Driving and Driving Safety
Off-road PSM
(PSM in Low Range off-road programme)
When the Low Range off-road driving programme
is active, an off-road PSM specially matched to off-
road driving is activated to enhance traction.
In order to improve driveability on difficult terrain,
the response of the off-road PSM is less sensitive
in the low speed range when the vehicle is
operated in the Low Range off-road driving
programme.
If the brakes are highly stressed, the automatic
brake differential (ABD) switches itself off to
protect the brakes. It remains deactivated until the
brake system has cooled sufficiently again.
Engine drag torque control (MSR)
In conditions of excessive slip, the engine drag
torque control system prevents all driven wheels
locking up when the vehicle is overrunning. This is
also the case for downshifts on a slippery road.
Switching off PSM
f Press PSM OFF button A.
PSM is switched off after a short delay.
The light-emitting diode in the button is lit up.
When PSM is switched off, the multi-functional
PSM light on the instrument panel lights up
and a message appears on the multi-purpose
display of the instrument panel.
During braking, the vehicle is stabilised even
when PSM is switched off.
One-sided spinning of the wheels is prevented,
even with PSM switched off.
PSM should always be switched on during
“normal” driving.
However, it may be advantageous to switch off
PSM temporarily in exceptional situations:
– On a loose surface and in deep snow,
– When “rocking the vehicle free” and
– When using snow chains.
Tiptronic vehicles: When PSM is switched off,
the slip monitoring function of Tiptronic is also
deactivated.
Driving and Driving Safety 195
– The multi-functional light on the instrument
panel lights up for a lamp check when the
ignition is switched on.
– The light indicates a control operation,
including when PSM is switched off (brake
control in the event of one-sided wheel spin).
– In conjunction with the multi-purpose display on
the instrument panel, the light indicates that
PSM is switched off.
– Faults are displayed by the light in conjunction
with the multi-purpose display of the instru-
ment panel.
PSM is out of order.
f Consult a qualified specialist workshop. We
recommend that you use a Porsche partner for
this work since these are staffed with trained
personnel and have the necessary parts and
tools.
Collapsible spare wheel
f Never switch off PSM when driving with a
collapsible spare wheel.
Towing
f For information on towing:
Please observe the chapter “TOWING AND
TOW-STARTING” on Page 356.
Tip on driving
When PSM is switched off, wheel-specific brake
interventions and the traction control system
(TCS) are also inactive.
The automatic brake differential (ABD) remains on.
Switching PSM back on
f Press PSM OFF button A.
PSM is switched on after a short delay.
The light-emitting diode in the button and the
multi-functional PSM light on the instrument
panel go out.
A message is shown on the multi-purpose
display of the instrument panel.
Multifunctional PSM light
196 Driving and Driving Safety
Vehicle-trailer combination stabilisation
(depending on country-specific vehicle equipment)
Vehicle-trailer combination stabilisation is an
assistance function for driving with trailers as part
of Porsche Stability Management (PSM).
Vehicle-trailer combination stabilisation detects
snaking of the vehicle-trailer combination.
If such critical driving situations are detected, the
vehicle-trailer combination stabilisation function
brakes the vehicle until the combination is stabi-
lised.
The vehicle-trailer combination cannot be stabi-
lised in all driving situations. Slippery roads or a
loose surface can cause the trailer to jackknife,
for example. Trailers with a high centre of gravity
can tip over.
f Steer carefully during the control process.
f For further information on driving with a trailer:
Please observe the chapter “DRIVING WITH A
TRAILER” on Page 244.
Danger!
Risk of accident.
In spite of the advantages of vehicle-trailer
combination stabilisation, it is still the
driver’s responsibility to adapt his driving
style and manoeuvres in line with road and
weather conditions, as well as the traffic
situation.
The increased safety that is provided should
not induce you to take greater risks with your
safety. The limits set by the physics of driving
cannot be overcome, even with vehicle-
trailer combination stabilisation.
Risks of accident due to inappropriate speed
cannot be reduced by vehicle-trailer combi-
nation stabilisation.
Risk of accident.
The vehicle-trailer combination cannot be
stabilised if the trailer jackknifes (e.g. on
slippery roads or on loose surfaces).
f Adjust your driving style to the road conditions.
Risk of accident.
Trailers with a high centre of gravity can tip
over.
f Adjust your driving style.
Risk of accident.
Excessive speed under the prevailing driving
conditions can lead to loss of control of the
vehicle-trailer combination.
f When using the vehicle with a trailer, drive at a
speed appropriate to road and traffic condi-
tions, as well as adjusted to the loading situa-
tion.
f Never exceed a speed of 80 km/h
(50 mph).
Driving and Driving Safety 197
Preconditions
– Trailer plug is plugged in,
– The trailer is in perfect technical condition.
Readiness for operation
– Vehicle-trailer combination stabilisation is
active when PSM is switched on.
f Observe country-specific laws for driving with
trailers.
Notes on operation
– Vehicle-trailer combination stabilisation is
switched off when PSM is switched off.
– When the brake pedal is pressed, vehicle-
trailer combination stabilisation is active even
if PSM is switched off.
– On vehicles with electrically folding trailer
hitch, the hitch must be fully extended and in
its end position.
198 Driving and Driving Safety
ABS brake system
(anti-lock brake system)
Safety notes!
In spite of the advantages of ABS, it is still the
driver’s responsibility to adapt his driving style and
manoeuvres in line with road and weather condi-
tions, as well as the traffic situation.
The increased safety that is provided should not
induce you to take greater risks with your safety.
The limits set by the physics of driving cannot be
overcome, even with ABS.
Risks of accident due to inappropriate speed
cannot be reduced by ABS.
ABS ensures
– Full steering control
The vehicle remains steerable
– Good driving stability
No skidding due to locked wheels
– Optimum braking distance
Shorter stopping distances in most cases
– Prevention of wheel locking
No flat spots on the tyres
Function
The decisive advantage of ABS is in the driving
stability and manoeuvrability of the vehicle in
hazardous situations.
The ABS prevents locking of the wheels during full
braking, on almost all road surfaces, until shortly
before the vehicle stops.
The ABS begins to control the braking process as
soon as a wheel shows a tendency to lock.
This controlled braking process is comparable
with extremely rapid cadence braking.
The pulsating brake pedal and a “juddering noise”
warn the driver to adapt his driving speed to the
road conditions.
f If full braking is necessary, fully depress the
brake pedal during the whole braking opera-
tion, even though the pedal is pulsating. Do not
reduce the braking pressure.
If the ABS warning lights light up on the instrument
panel and on the multi-purpose display of the
instrument panel while the engine is running, ABS
has switched off because of a fault.
In this case, the braking system will operate
without lock prevention, as in vehicles without
ABS.
f Adapt your driving style to the changed
braking behaviour.
The ABS system must be checked immediately
in order to prevent the occurrence of further
faults with effects which cannot be defined.
Consult a qualified specialist workshop. We
recommend that you use a Porsche partner for
this work since these are staffed with trained
personnel and have the necessary parts and
tools.
The ABS control unit is adjusted for the approved
tyre dimensions.
The use of tyres with non-approved dimensions
can lead to different wheel speeds, causing ABS
to switch off.
Warning light
Driving and Driving Safety 199
Off-road ABS
(ABS in Low Range off-road programme)
When the Low Range off-road driving programme
is active, an ABS configuration specially matched
to off-road driving is activated automatically.
In the event of braking on loose ground, the
permissible slip values for ABS braking are
increased so that the off-road braking distance is
reduced (wheels dig into the surface).
If the driver needs to steer, this off-road driving
programme is automatically switched off to
maintain steerability.
Hillholder –
moving-off assistant on vehicles with
Tiptronic S
In Tiptronic selector lever positions D and M, the
hillholder function makes it easier to move off
from a stand-still on an upward slope when the
engine is running. The driver does not have to
apply the brake.
The hillholder function is not active:
– In Tiptronic selector lever positions N and R,
– In the reduced driving programme and
– If not all of the wheels are touching the ground
(on difficult terrain, for example).
f For further information on moving off with the
hillholder function on vehicles with Tiptronic S:
Please observe the chapter “STOPPING” on
Page 181.
Safety notes!
In spite of the advantages of the hillholder
function, it is still the driver’s responsibility to
adapt his driving style and manoeuvres in line with
the prevailing conditions.
The increased safety that is provided should not
induce you to take greater risks with your safety.
The limits set by the physics of driving cannot be
overcome, even with the hillholder function.
Driving in limit situations should be avoided, e.g.
on icy slopes or on slippery surfaces. Assistance
by the hillholder is not guaranteed in these and
similar cases.
200 Driving and Driving Safety
Porsche Drive-Off Assistant –
Moving-off assistant on vehicles with
manual transmission
The Porsche Drive-Off Assistant is an assistance
function which helps the driver move off on
upward slopes. The vehicle must have sufficient
road contact.
The Porsche Drive-Off Assistant is available for
slopes with a gradient as from around 5 %.
Danger!
Risk of accident.
Assistance by the Porsche Drive-
Off Assistant is not guaranteed when moving
off on a slippery surface (e.g. on icy or loose
surfaces). In this case, the vehicle could slip.
The limits set by the physics of driving cannot
be overcome, even with the Porsche Drive-
Off Assistant. The responsibility for moving
off on upward slopes is still the driver’s
despite the Porsche Drive-Off Assistant.
f Always adjust your driving style to the driving
conditions and vehicle load, use the footbrake
if necessary.
Moving off with Porsche Drive-Off Assistant
1. Hold the vehicle securely on the slope with the
footbrake or parking brake.
The engine must be running.
2. Fully depress the clutch pedal.
3. Engage a gear corresponding to the direction
of travel up the slope (1st gear or reverse
gear).
4. While keeping the clutch pedal depressed,
release the footbrake or foot-operated parking
brake.
The vehicle is held on the slope.
5. Move off as usual.
Note on operation
The Porsche Drive-Off Assistant is not active:
– In the event of shift to neutral.
– When changing gears.
– If the engine is not running.
Danger!
Risk of accident.
If the Porsche Drive-Off Assistant is not
active, the vehicle will no longer be held on
the slope.
f Hold the vehicle with the footbrake.
Driving and Driving Safety 201
Engine Braking Support
(assistance when driving downhill)
The Engine Braking Support system is an assist-
ance system which helps the driver when driving
slowly downhill at speeds up to approx. 20 km/h
(12 mph), e.g. on steep slopes or on wintry
mountain roads.
Engine Braking Support is active and brakes the
vehicle as long as the accelerator is not used
when travelling downhill.
If road grip is lost on one or more wheels, the
system brakes the wheels which have good road
contact.
Like all brakes, the braking ability of the Engine
Braking Support system is impaired by slippery
surfaces (e.g. on icy or loose surfaces).
Warning!
Risk of accident. Reduced braking ability on
a slippery surface.
f Always adjust your driving style to the driving
situation.
Preconditions:
– The accelerator must not be used when travel-
ling downhill.
– The speed must not exceed approx. 20 km/h
(12 mph).
– Vehicles with Tiptronic S: Tiptronic selector
lever position D, M or R must be engaged.
– Vehicles with manual transmission: A gear
must be engaged (1st – 6th or R). The clutch
pedal must not be used when travelling
downhill.
Tip on driving
The Engine Braking Support system is active when
driving downhill either forwards or backwards.
Checks on test stands
Brake tests
Brake tests must be carried out only in the High
Range on-road driving programme and on plate-
type or roller test stands.
The following limit values must not be exceeded
on roller test stands:
– Test speed 7.5 km/h (4.7 mph)
– Test duration 20 seconds
Parking brake test
Parking brake tests on the brake test stand must
be performed only with the ignition switched off
and with the Tiptronic selector lever in position N
or with the gearshift lever in neutral position.
Balancing wheels on the vehicle
During finish balancing of the wheels, the entire
vehicle must be lifted and the wheels must be free
to turn.

Related Topics

Driving and Driving Safety
Before driving off Tips for running in Ignition lock/steering lock Starting and stopping the engine Parking brake Footbrake Brief overview ? cruise control Cruise control Manual transmission, clutch Tiptronic S Selector lever positions Driving programmes for on-road and off-road driving Air suspension with level control and height adjustment Porsche Active Suspension Management (PASM) Porsche Dynamic Chassis Control (PDCC) Off-road driving Driving systems for off-road driving Uphill driving Airbag systems

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