Porsche 928 Workshop Manual page 615

Fuel System I Electronic Control
Fault, Fault Code
Possible Causes, Elimination, Remarks
Test point 7
Knock sensor I
Fault code 2-31
Switch on the ignition.
Display: approx. 5 V
Connect the ohmmeter to terminals 1 and 2 on the plug side
Note
The switch is checked with the engine running. Apply the handbrake
and operate the foot brake. Comply with relevant safety regulations.
Display in position P or N:
m Ohm (switch open)
Display in position D:
< 1 Ohm (switch closed).
If these values are not reached, measure directly at the switch or
renew.
Knock sensor I: sensor signal is not plausible. Check:
- Knock sensor mounting (note tightening torque
and type of screw)
- Wiring and plug connections according to wiring diagram
Reconnect the sensors to eliminate contact resistance.
- Is any coolant or other fluid present at the knock sensors?
- Renew knock sensor
If the knock sensor is faulty, the ignition will be retarded (safety cir-
cult).
D20-8
EZK-Diagnosis/Troubleshooting
Printed in Germany - XXV 1990