P0331

DIAGNOSTIC CODE PO331
Knock sensor for cyl. 2-4-6, input to control module absent/no continuity or short circuit.

Fault Symptom.
Engine performance may be down.

Condition
The input from the knock sensor is active or absent for more than four seconds at engine speeds above 1800 rpm.

Diagnostic Procedure.
1. Use the ISAT command "KNOCK CONTR ACTIVE" in the "READ ON/OFF" menu or the "KNOCK CONTROL" command in the "READ FUNCTIONS" menu while driving the car with the engine laboring heavily.

The ISAT should then show how many degrees the control module retards the ignition when knocking occurs.

If ignition retardation takes place, proceed to step 7.
If no retardation of the ignition is shown in spite of the engine being made to work hard, continue with the next point.

2. Check that the knock sensor connector makes good contact.

3. With the ignition switched OFF, connect a BOB between the MOTRONIC control module and the wiring.

Start the engine and check the knock sensor's signal voltage by taking a reading across 29 and 30 on the BOB. When the engine is revved up, the voltage should be higher than 20 mV AC.

If the voltage is OK, proceed to step 5.
If it is not, continue with step 4.

4. Check the screened lead between the knock sensor and pin 29 of the control module for continuity/shorting.





5. Check that the knock sensor is tightened to a torque of 22 Nm (16 ft lb).

6. Then check the knock sensor signal by measuring the voltage directly on the sensor while lightly tapping the knock sensor retaining screw. The voltage should then go up to at least 100 mV AC.

If no voltage is obtained (the knock sensor appears to be completely "dead"), change the sensor.

7. Clear all trouble codes and drive the car on the road to check whether any codes are generated afresh.

If they are, continue at "Before Replacing Control Module" for further diagnostic instructions. Before Replacing A Control Module