GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2007 🢒 Ascender - 2WD 🢒 DTC 🢒 DTC P0325

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 provide an overview of each diagnostic category.

DTC Descriptor

DTC P0325: Knock Sensor (KS) Circuit

Diagnostic Fault Information

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

Knock Sensor Signal

P0327, P0332

P0325

P0325

P0327, P0332

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

DTC P0325 runs continuously when:

    • The engine speed is equal to or greater than 1,800 RPM.
    • The engine coolant temperature (ECT) is greater than -40°C (-40°F).
    • The engine run time is greater than 1 second.

Conditions for Setting the DTC

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

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.
    • The KS must be clear of hoses, brackets, and engine electrical wiring.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

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

Electrical Information Reference

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

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Output Controls

Circuit/System Testing
  1. Ignition ON, engine OFF.
  2. Disconnect the KS harness connector.
  3. Measure for 3-5 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.

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.

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