GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The knock sensor (KS) system enables the powertrain control module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The KS is located on the intake side of the engine block. The KS produces an AC voltage signal that varies depending on the vibration level during engine operation. The PCM adjusts the spark timing based on the amplitude and the frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM learns a minimum KS noise level at idle and uses calibrated values for the rest of the RPM range. The PCM should monitor a normal KS signal within the noise channel. If the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system, or the KS signal is not present, DTC P0325 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0325 Knock Sensor (KS) Circuit

Conditions for Running the DTC

    • The engine speed is more than 1,800 RPM.
    • The engine load meets or exceeds a calibrated specification.
    • DTC P0325 runs continuously when the above conditions are met.

Conditions for Setting the DTC

The average KS voltage is less than 0.01 volts or more than 4.9 volts for 8 seconds.

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.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  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 Detonation/Spark Knock

3

  1. Turn OFF the ignition.
  2. Disconnect the knock sensor (KS).
  3. Measure the resistance from the KS signal circuit on the sensor side of the KS harness connector to a good ground with the DMM.
  4. Measure the resistance from the KS low reference circuit on the sensor side of the KS harness connector to a good ground with the DMM.

Does the DMM display an open for both circuits?

--

Go to Step 4

Go to Step 7

4

  1. Turn ON the ignition, with the engine OFF.
  2. On the powertrain control module (PCM) side of the KS harness connector, measure the DC voltage from the KS signal circuit to a good ground with a DMM.
  3. On the PCM side of the KS harness connector, measure the DC voltage from the KS low reference circuit to a good ground with a DMM.

Is the voltage more than the specified value on any circuit?

4.2 V

Go to Step 5

Go to Step 6

5

  1. Turn OFF the engine.
  2. Disconnect the PCM.
  3. Test the KS signal circuit or the KS low reference circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

6

  1. Turn OFF the engine.
  2. Disconnect the PCM.
  3. Test the KS signal circuit and the KS low reference circuit for an open, a high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

7

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

Did you find and correct the condition?

--

Go to Step 11

Go to Step 9

8

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

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

9

Replace the KS. Refer to Knock Sensor Replacement .

Did you complete the replacement?

--

Go to Step 11

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10

Replace the PCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 11

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11

  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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 12

12

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

System OK