Knock Sensor: Description and Operation

Knock Sensor:

DESCRIPTION
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.

OPERATION
To control spark knock, a Knock Sensor (KS) system is used. This system is designed to retard spark timing up to 15 degrees to reduce spark knock in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

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 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 sensors and circuitry. If the PCM is replaced, the KS module needs to be transferred from the original PCM. If the KS module is missing or faulty causing a continuous knock condition to be indicated, the PCM will set DTC P0325.

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.