For 1990-2009 cars

### Purpose

Varying octane levels in today's gasoline may cause detonation in some engines. Detonation is caused by an uncontrolled explosion (burn) in the combustion chamber. This uncontrolled explosion could produce a flame front opposite that of the normal flame front produced by the spark plug. The rattling sound normally associated with detonation is the result of two or more opposing pressures (flame fronts) colliding within the combustion chamber. Though light detonation is sometimes considered normal, heavy detonation could result in engine damage. To control spark knock, a Knock Sensor (KS) system is used. This system is designed to retard spark timing when spark knock is detected in the engine. The KS system allows the engine to use maximum spark advance for optimal driveability and fuel economy.

### Operation

The KS system has two major components:

• | The KS module.

• | The knock sensor(s).

The PCM contains a replaceable Knock Sensor (KS) module. The KS module contains the circuitry that allows the PCM to diagnose the knock sensors and circuitry

The knock sensor(s) detect abnormal vibration (spark knocking) in the engine. The knock sensor(s) are mounted in the engine block near the cylinders. The knock sensor(s) produce an AC output voltage which increases in amplitude and frequency with increased severity of detonation. This signal voltage is input to the PCM. The PCM then adjusts the Ignition Control (IC) timing to reduce spark knock. The knock sensors are used to detect engine detonation, allowing the PCM to retard Ignition Control (IC) spark timing based on the KS signal being received.

### Diagnosis

If the KS module is missing or faulty causing a continuous knock condition to be indicated, the PCM will set DTC P0325.

The scan tool has four data display parameters available for diagnosing the KS system. The four parameters are described as follows:

• | KS Active Counter is used to monitor the input signal from the knock sensor. This parameter will increment while detonation is being detected.

• | Knock Retard is the indication of how much the PCM is retarding the spark. The PCM will retard spark in response to any of the following conditions:

- | An active knock sensor system DTC is set.

- | The knock sensor signal is indicating detonation.

- | The traction control system desired torque signal is indicating a traction control event.

• | KS Minimum Learned Noise indicates the minimum level that the PCM has detected on the noise channel while the noise level was being learned. The PCM uses this parameter for diagnosis of the KS system.

• | KS Noise Channel indicates the current voltage level being monitored on the noise channel. The PCM monitors the noise channel level to ensure that the KS sensors, the KS module, and the related wiring is operating correctly. If the voltage level on the KS noise channel circuit is below the range considered normal, DTC P0327 will set, indicating a fault in the KS circuit or one of the knock sensors.

DTCs P0325, P0326, and P0327 are designed to diagnose the KS module, the knock sensors, and related wiring, so problems encountered with the KS system should set a DTC.