[928uk] Porsche PSD System

[George Layton]

A couple of weeks ago someone on the list was asking about the operation
of the PSD system.

As I have just learnt how to use the OCR software that came with my
scanner, below is the page from the Driver's Manual for my GTS which
describes the operation of the system.

Porsche Limited-slip Differential (PSD)

The PSD is an electronically controlled differential lock which switches
on automatically without intervention from the driver.

It is an aid to driving off on road surfaces with varying degrees of
traction and serves to improve driving stability when cornering with
high lateral acceleration.

In spite of this the driver must still take the responsibility for
adjusting his driving actions to road and weather conditions, and to the
traffic situation. The increased safety offered by the system should not
induce you to take increased risks.

Aid for Driving Off

The PSD cuts in whenever a speed difference (slip) of more than 2 km
(1.25 mph) occurs at the drive wheels and the speed of the vehicle is no
higher than 30 km/h (19 mph). The extent of the differential locking
effect is determined by the slip of the drive wheels. However, some spin
by both drive wheels cannot be avoided if acceleration is too severe.

Acceleration out of Corners

The PSD cuts in over the entire speed range whenever the control unit
receives a high lateral acceleration signal when accelerating out of
corners and the inside wheel shows signs of spinning.

The lock transmits the non-transferable driving force of the inside
wheel to the outside wheel.

If both wheels start to spin, the lock is disengaged for safety reasons.

Deceleration in Corners

If the control unit receives a high lateral deceleration signal at
speeds of over 60 km/h (37 mph), a limited-slip torque is also built up
when decelerating in corners to counteract oversteer.

Note

A solenoid valve regulates the gentle build-up and reduction of the
limited-slip torque. The audible timing noise indicates that PSD
regulation is occurring.

Should the control unit detect a fault in the limited-slip differential,
the PSD is switched off for safety reasons and a fault is indicated in
the display of the information system.

You should have your PSD tested at an Official Porsche Centre as soon as
possible! The switching-off of your PSD changes the driving
characteristics of the vehicle.

The switching-off of the ABS system always results in the PSD being
switched off, too.

The PSD indicator light in the instrument cluster comes on while the
limited-slip differential is activated or if both drive wheels start to
spin.

George.


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