GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Cobalt 🢒 DTC 🢒 DTC P0325, P0326, P0327, or P0328

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0325: Knock Sensor (KS) Circuit

DTC P0326: Knock Sensor (KS) Performance

DTC P0327: Knock Sensor (KS) Circuit Low Voltage

DTC P0328: Knock Sensor (KS) Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

Knock Sensor Signal

P0327, P0328

P0325

P0325

P0327, P0328

P0326

Circuit/System Description

The knock sensor (KS) system enables the control module 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 control module receives the KS signal through 2 isolated signal circuits. The control module adjusts the spark timing based on the amplitude and the frequency of the KS signal.

Conditions for Running the DTC

P0325

This DTC runs continuously when:

    • The engine speed is greater than or equal to 1,500 RPM.
    • The engine coolant temperature (ECT) is greater than -40°C (-40°F).
    • The engine run time is greater than 1 second.
    • DTCs P0327 or P0328 are not set.

P0326

This DTC runs continuously when:

    • The engine speed is greater than or equal to 1,800 RPM.
    • The manifold absolute temperature (MAP) is greater than 55 kPa.
    • DTCs P0120, P0121, P0122, or P0123 are not set.

P0327, P0328

This DTC run continuously when:

    • The ECT is greater than -40°C (-40°F).
    • The engine run time is greater than 1 second.

Conditions for Setting the DTC

P0325

The KS signal circuits are open or shorted together for 6 seconds.

P0326

    • The KS signal indicates an excessive engine knock is present.
    • The control module commanded spark retard at a given engine load and speed is more than the calibrated value.
    • The above conditions exist for 6 seconds.

P0327 and P0328

The KS signal circuits are shorted to ground or power.

Action Taken When the DTC Sets

DTC P0325, P0326, P0327, and P0328 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTC P0325, P0326, P0327, and P0328 are Type B DTCs.

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.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Controls Connector End Views
    •  Engine Control Module Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Measuring Frequency
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Output Controls
    •  Scan Tool Data Definitions

Circuit/System Testing

P0325, P0327 and P0328

    Important: If the KS lead is damaged in any way, replace the KS.

  1. Ignition ON, engine OFF.
  2. Disconnect the KS harness connector.
  3. Measure for 2-5 volts between each of the following circuits and ground on the engine control module (ECM) side of the harness connector:
    4. • The KS signal circuit, terminal A
    • The KS signal circuit, terminal B
    ⇒If less than the specified range, test the circuits for a short to ground or an open/high resistance. If the circuits test normal, replace the ECM.
    ⇒If greater than the specified range, test the circuits for a short to voltage. If the circuits test normal, replace the ECM.
  4. If the circuits test normal, replace the KS.

P0326

       Important: If DTC P0327, P0328, P0335, P0336 are also set, diagnose those DTCs first.

    • Inspect for a loose or broken vehicle accessory or accessory bracket.
    • Inspect for excessive engine mechanical noise.

Component Testing
  1. Connect the DMM from the KS signal circuit terminal A to the KS signal circuit terminal B on the sensor side of the KS harness connector.
  2. Set the DMM to the 400 mV AC hertz scale and wait for the DMM to stabilize at 0 Hz.

    3. Important: DO NOT tap on plastic engine components.

  3. Tap on the engine block with a non-metallic object near the KS while observing the signal indicated on the DMM.
  4. The DMM should display a fluctuating frequency while tapping on the engine block.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References for ECM replacement, setup, and programming
    •  Knock Sensor Replacement
    •  Symptoms - Engine Mechanical
    •  Symptoms - Engine Controls