Porsche 928 Workshop Manual page 580

928 S4
928 GT Fuel System - Electronic Control
24128
Control units
The LH and EZK control units were given diagnostic capability at the end of the 1968 model year
(see 1986 Model Information, Fuel and Ignition System _ Diagnosis).
Starting with the 1986 model year, self-diagnosis with a fault memory is integrated into the two fuel
injection and ignition control units. This makes it possible to identify and store certain malfunctions of
the fuel injection and ignition system and of the knock regulating system.
To make sure that faults identified and stored in this way are not erased when the ignition is turned
off, a permanent + signal is supplied to both control units.
Important:
If the control unit plugs or the battery are disconnected, the fault memory will be erased
Diagnostic tester:
To call up the contents of the fault memory on 1988 model cars a new diagnostic taster (special tool
number 9268) was developed. It is connected to an existing plug connection on the control unit
mounting plate.
For diagnostic work on cars from the 1989 model year on, a 19.pin plug-in connection under the
booster cover is connected to the new 9286 system tester or the 9268 flashing code tester (using an
intermediate adapter lead).
Note:
The test point concerned is supplemented by the equivalent flashing fault code on the 9266 tester.
Example:
Test point 2 = idle speed contact (l-12)
2nd digit display:
"1" = fault present, or
"2" = no fault present.
From tester module version 2.0 on, actual engine data can be read out from the EZWcontrol unit with
system tester 9288.
DME Diagnosing/Troubleshooting
Prinled In Germany - XXV, 1990
D 24128 - 5