Knock Sensor: Description and Operation

The knock sensor detects abnormal vibration (spark knocking) in the engine. The sensor is located on the engine block near the cylinders. The sensor produces an AC 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. DTC P0325 knock Sensor System DTC P0327 Knock Sensor (KS) Circuit are designed to diagnose the PCM, the knock sensor, and related wiring, so problems encountered with the KS system should set a DTC.

Refer to Knock Sensor System Description for a description of the knock sensor system.

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.

The PCM calculates an average voltage the knock sensor signal and takes instantaneous signal voltage readings. The PCM uses the instantaneous signal voltage reading to determine the state of the knock sensor circuitry. If the knock sensor system is operating normally, the PCM should monitor instantaneous KS signal voltage readings varying outside a voltage range above and below the calculated average voltage. The following DTCs are used to diagnose the knock sensor system:
^ If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 Knock Sensor System will set.
^ DTC P0327 is designed to diagnose the knock sensor, and related wiring, so problems encountered with the KS system should set a DTC. However, if no DTC was set but the KS system is suspect because detonation was the customer's complaint, use the tables for DTC P0327 Knock Sensor (KS) Circuit to diagnose the Detonation/Spark Knock Symptom.