Porsche 928 Workshop Manual page 622

928 S4
928 GT Fuel System / Electronic Control
28
d) Check output stage control signal
Check at both (disconnected) output stage
plugs.
Connect the positive tester lead to terminal 5
and the negative tester lead to terminal 2 of
the disconnected output stage plug.
Crank the engine with the starter motor.
The oscilloscope must display a control signal
for each output stage plug.
Test point 16: leads K and L
The diagnostic connection between the EZK
control unit and the diagnosis tester is by way
of the two leads K and L. If diagnosis is not
possible, perform the following checks:
1. Continuity test (refer to wiring diagram)
la&L: Pin 7 (19-pole diagnosis socket)
- Pin 7 (EZK plug)
&&K: Pin 8 (19.pole diagnosis socket)
- Pin 1 (EZK plug)
2. Ground short test (refer to wiring diagram)
U: The voltage at Pin 7 (19.pole diagnosis
socket) must be > 8 V with the ignition
switched on.
t,eag.K: The voltage at Pin 8 (19-pole diagno-
sis socket) must be > 8 V with the ignition
switched on.
Possible causes of faults:
. Short to ground or break in wiring or plug
connections.
. A faulty control unit connected to these
lines (it may be any control unit with diagno-
sis capability, not necessarily the EZK con-
trol unit).
- Checking: disconnect plugs successively at
the control units with diagnosis capability
until the voltage becomes z- 8 V. Renew
the control unit which is causing the fault.
- Faulty tester.
. No power supply at diagnostic plug.
No ground at diagnostic plug.
EZK-Diagnosis/Troubleshooting
Printed In Germany - XXV, ,930
D28-15