GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 DTC P0325 or P0330

Circuit Description

The knock sensor (KS) system enables the engine control module (ECM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The KS produces an AC signal that varies at all engine speeds and loads. The ECM makes adjustments to the spark timing based on the amplitude and frequency of the KS signal. The ECM receives the KS signal through a signal circuit. The KS ground is supplied by the ECM through a low reference circuit. The ECM uses the KS to calculate the amount of normal engine noise (a noise channel) for a wide range of engine speeds and loads. The ECM compares the actual KS signal to the learned noise channel. The ECM uses the noise channel in order to diagnose the KS and the related wiring. If the ECM detects a loss of the noise channel, a diagnostic trouble code (DTC) will set. DTC P0325 refers to the bank 1 sensor. DTC P0330 refers to the bank 2 sensor.

Conditions for Running the DTC
    • DTCs P0315, P0335, P0336, P0340, P0341, P0345, P0346, P0365, P0366, P0390, or P0391 are not set.
    • The engine speed is more than 1,400 RPM.
    • The engine load meets or exceeds a calibrated specification.

Conditions for Setting the DTC

The ECM detects a KS signal that is out of the calibrated range.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • Inspect the KS for physical damage. A KS that is dropped or damaged may cause a DTC to set.
    • Inspect the KS for proper installation. A KS that is loose or over torqued may cause a DTC to set. The KS should be free of thread sealant. The KS mounting surface should be free of burrs, casting flash, and foreign material.
    • For an intermittent condition, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. If the KS signal circuit or the KS low reference circuit is shorted to voltage, the KS may still produce a signal.

    2.

  2. If the KS signal circuit or the KS low reference circuit is shorted to ground, the KS may still produce a signal.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important: If an engine mechanical noise can be heard, repair the condition before proceeding with this diagnostic. Refer to Symptoms - Engine Mechanical in Engine Mechanical - 4.6L.

  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM).
  3. Connect a DMM between the affected knock sensor (KS) signal circuit and the KS low reference circuit.
  4. Set the DMM to the 400 mV AC hertz scale and wait for the DMM to stabilize at 0 Hz. Refer to Measuring Frequency in Wiring Systems.

    5. Important: Do not tap on plastic engine components.

  5. Observe the DMM while tapping on the engine block with a non-metallic object.

Does the DMM display a fluctuating frequency while tapping on the engine block?

Go to Step 4

Go to Step 7

4
  1. Set the DMM to the ohm scale.
  2. Measure the resistance from the KS signal circuit to a good ground with the DMM.
  3. Measure the resistance from the KS low reference circuit to a good ground with the DMM.

Does the DMM read OL?

Go to Step 5

Go to Step 6

5

Important: Disconnection of the ECM during testing may eliminate the voltage source that caused this fault.

Test the affected KS signal circuit or the KS low reference circuit for a short to power or a short to another ECM circuit.

Did you find and correct the condition?

Go to Step 14

Go to Step 11

6

Important: Disconnection of the ECM during testing may eliminate the ground source that caused this fault.

Test the KS signal circuit or the KS low reference circuit for a short to ground or a short to another ECM circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 11

7
  1. Remove the fuel injector sight shield. Refer to Fuel Injector Sight Shield Replacement in Engine Mechanical - 4.6L.
  2. Disconnect the 12-way connector at the right rear of the engine.
  3. Test the affected KS signal circuit and the KS low reference circuit between the 12-way connector and the ECM for the following conditions:
    4. • An open
    • A high resistance
    • The signal circuit and low reference circuit shorted together

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 8

8

Test for an intermittent and for a poor connection at the 12-way connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 9

9
  1. Remove the intake manifold. Refer to Intake Manifold Replacement in Engine Mechanical - 4.6L.
  2. Test the affected KS signal circuit and the KS low reference circuit between the 12-way connector and the KS for the following conditions:
    3. • An open
    • A high resistance
    • The signal circuit and low reference circuit shorted together

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 10

10

Test for an intermittent and for a poor connection at the affected KS. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 12

11

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 13

12

Replace the affected KS. Refer to Knock Sensor 1 Replacement or Knock Sensor 2 Replacement .

Did you complete the replacement?

Go to Step 14

--

13

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

Go to Step 14

--

14
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

Go to Step 2

Go to Step 15

15

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK