Check Hydraulics Of The Lock/Troubleshooting - Porsche 928 Workshop Manual

39
Differential. transaxle svstem
928
Check hydraulics of the lock
This comprises: check of the lock hydrau-
lics without pressure gauge (special tool
9509).
Precondition
Read
out DTC memory with system tester
9288. No fault
stored.
1. Jack up the vehicle on one side until a rear
wheel can be turned freely.
2. Switch on system tester 9288. Select lock
test (system PSDl Drive Links menu).
Pulse transverse lock (pressing function key
I on tester once = 1 pulse) and simulta-
neously turn the rear wheel.
The wheel must be completely fixed
(locked) after several pulses.
Caution:
If the vehicle is fully raised, hold
the opposite rear to keep it from turning.
If the wheel does not lock, continue with
troubleshooting "System depressurized".
If the wheel does lock, continue with trou-
bleshooting: System pressure present.
Troubleshooting
If the system is depressurized, the follo-
wing faults are possible:
- Brake fluid reservoir (No. 12) empty
(system leaks).
- Voltage supply for high-pressure pump
(No. 1) not OK (check pump relay No. 38
and fuse in the luggage compartment).
- Pressure warning switch (No. 2) not OK.
Test on Page D39-251 ff.
- High-pressure pump (No. 1) defective.
Check pump operation by bridging terminals
30 and 87 on the pump relay (in the lug-
gage compartment).
Important:
Pump operating time when brid-
ging the terminals max 3 seconds. (Per-
form test only once.)
- Mechanical
defect of lock solenoid valve
(No. 9).
The following faults are possible if system
pressure is present:
- Pressure warning switch (No. 2) not OK
- Electrical wire for activating the fault display
"PSD off not OK (check in combination
with the wiring diagram).
- High-pressure pump no longer operates (de-
fect,
or voltage
supply not OK), but there is
still a residual pressure of less than 107 bar
in the system. This pressure is reduced
each time the pump is operated.
D39 - 240
a
PSD diagnosis/Troubleshooting
Printed in Gemny - XXXV, 1985