Porsche 928 Workshop Manual page 592

928 S4
928 GT Electronic Fuel Injection
24
Fault, Fault Code Possible Causes, Elimination, Remarks
Break (m Q): The LH control unit reverts to a fixed,
previously stored program. If the engine
is warm, there is no mixture enrichment.
If the engine is cold, however, this causes
starting problems (since there is no
cold-start enrichment).
Short circuit (0 Q): When the engine is cold it does not
respond to the throttle being opened;
the mixture is too weak and the engine
stallsNo effect at regular operating
temperature.
Test point 5
l
Air mass sensor
Fault code l-21
a) Power supply (V)
Disconnect the plug at the air mass sensor and connect the voltme-
ter to plug terminals 2 and 4 using the test leads.
Use the test leads to connect terminals 17 and 21 on the LH control
unit plug after it has been disconnected.
Display: battery voltage
No display:
Remove LH relay XXV and bridge terminals 87 and 30 at the relay
base. Display on voltmeter connected to air mass sensor plug:
battery voltage.
If there is a battery voltage display, check the LH relay and its activa-
tion.
If there is no display, check leads and plug connections according to
wiring diagram.
b) Checking resistance of hot wire circuit at the
air mass sensor (9)
Disconnect the plug connection at the air mass sensor. Connect ter-
minals 3 and 5 at the air mass sensor with the ohmmeter.
Display: 3.8 - 4.10
LH-Diagnosis/Troubleshooting
Printed in Germany - Xxv, ,990
D 24 - 15