Knock Sensor System Diagnosis

Circuit Description
The knock sensor (KS) sends an AC voltage signal to the powertrain control module ([1][2]PCM). As the KS detects engine knock, the signal to the PCM changes in amplitude and frequency. The PCM retards timing if the engine speed is over 900 RPM.

Diagnostic Aids
If the KS system checks OK, but detonation is the complaint, refer to Diagnosis, Detonation/Spark Knock.

Test Description
Number(s) below refer to the step number(s) in the Diagnostic Test:

9. The change in signal speed depends on how hard the tapping is done. Normally there is about 1.5 to 10 mV at [1][2]PCM pin A2 with the engine off. Loud tapping should be able to make the reading jump to 20-25 mV AC.

Diagnostic Test
1. Is DTC P0325 or P0327 set?

[YES] Go to DTC P0325 or DTC P0327.
[NO] Go to Step 2.

3. a. Run the engine at 1500 RPM.
b. Is there an internal engine knock?

[YES] Go to Step 3.
[NO] Go to Step 4.

4. a. Repair the mechanical problem.
b. Is the action complete?

[YES] Verify repair.

5. a. Replace the [1][2]PCM.

IMPORTANT: The replacement [1][2]PCM must be programmed.

b. Is the action complete?

[YES] Verify repair.

6. a. Start the engine.
b. Monitor the knock retard display on the scan tool while changing the throttle setting to place different loads on the engine.
c. Is knock retard at the specified value? (Turn the ignition "OFF.")

[VALUES] 0°

[YES] Go to Step 9.
[NO] Go to Step 7.

7. a. At the rear of the engine, behind the rear fuel injector on the lift side, disconnect the 2-wire knock sensor harness connector.
b. Attach the positive lead of DVM to B+.
c. On the main harness side of the connector, use the negative lead of the DVM to probe the connector pin that is connected to the black wire.
d. Does the DVM indicate the specified value? (Reconnect the knock sensor harness.)

[VALUES] B+

[YES] Go to Step 9.
[NO] Go to Step 8.

8. Repair the open black wire ground for the shield which prevents stray electromagnetic pulses from affecting the knock signal.

[YES] Verify repair.

9. a. Reconnect the wire harness if it was previously disconnected in Step 7.
b. Set a DVM to AC voltage.
c. With the DVM, backprobe the [1][2]PCM connector at A2.
d. Tap the engine lift bracket with a socket extension.
e. Did the DVM show an increase in AC voltage while tapping on the lift bracket?

[YES] System OK.
[NO] Go to Step 10.

10. Replace the knock sensor.

[YES] Verify repair.