Knock Sensor System

Purpose
Varying octane levels in todays 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 up to 20 to reduce spark knock in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.


Operation
The KS system has two major components:

^ KS module.

^ Knock sensor.

The knock sensor detects abnormal vibration (spark knocking) in the engine. The sensors are mounted in the engine block near the cylinders. The sensors produce an IAC output voltage which increases with the severity of the knock. This signal voltage is input to the PCM. The PCM then adjusts the Ignition Control (IC) timing to reduce spark knock.

The knock sensor is used to detect engine detonation, allowing the PCM to retard Ignition Control (IC) spark timing based on the KS signal being received. The knock sensor produces an IAC signal which rides on a 5 volts DC signal supplied by the PCM. The signal amplitude and frequency is dependent upon the amount of knock being experienced.

The PCM contains a replaceable Knock Sensor (KS) module. The KS module contains the circuitry that allows the PCM to utilize the KS signal and diagnose the KS sensor and circuitry. If the KS module is missing or faulty causing a continuous knock condition to be indicated, the PCM will set DTC P0325.

The PCM determines whether a KS system fault is present by monitoring The voltage level on the KS noise channel at various engine speeds. Normal engine noise varies depending on engine speed and load. If the voltage level on the KS noise channel voltage is below the range considered normal, DTC P0327 will set, indicating a fault in the KS circuit or the knock sensor. If the PCM determines that an abnormally high noise channel voltage level is being experienced, a DTC P0326 will set.