For 1990-2009 cars

### 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 Descriptors

DTC P0325: Knock Sensor (KS) Circuit
DTC P0326: Knock Sensor (KS) Performance

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
Knock Sensor Signal | P0325 | P0325 | P0325 | P0325 | P0326

### Circuit/System 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 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 ECM receives the KS signal through a signal circuit and a low reference circuit. The ECM adjusts the spark timing based on the amplitude and the frequency of the KS signal.

### Conditions for Running the DTC

These DTCs run continuously when:

• | DTCs P0335, P0336, P0340, P0341, P0365, P0366, P0601, P0602, or P0604 are not set.

• | The engine speed is greater than 2,500 RPM.

• | The mass air flow (MAF) is greater than 20 g/s.

• | The engine is NOT in decel fuel cut-off.

### Conditions for Setting the DTC

#### P0325

The KS signal voltage is above or below a calibrated range for 20 engine revolutions.

#### P0326

The KS signal is not present for 20 engine revolutions.

### Action Taken When the DTC Sets

DTCs P0325 and P0326 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0325 and P0326 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

Component Connector End Views

#### Description and Operation

Knock Sensor (KS) System Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition ON, engine OFF.
2. Disconnect the KS harness connector.
3. Measure for 2-5 volts between the signal circuit terminal 1 and ground on the ECM side of the harness connector.

⇒ | 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. Measure for less than 5 ohms between the low reference circuit terminal 2 and ground.

⇒ | If greater than the specified range, test the circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

5. If the circuits test normal, replace the KS.

### Component Testing

1. Connect the DMM between the KS signal circuit terminal 1 and the low reference circuit terminal 2 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.

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

• | Symptoms - Engine Controls

• | Symptoms - Engine Mechanical

• | Control Module References for ECM replacement, setup, and programming