Knock Sensor System

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.

Powertrain Control Module (PCM):

OPERATION
The PCM contains integrated Knock Sensor (KS) diagnostic circuitry. Input signals from the knock sensor are used to detect engine detonation, allowing the PCM to retard Ignition Control (IC) spark timing based on the amplitude and frequency of the KS signal being received.

The knock sensor detects an abnormal vibration (spark knocking) in the engine. The knock sensor is mounted in the engine block near the cylinders. The knock sensor produces an AC signal voltage under all engine operating conditions. During engine operation, the PCM calculates the average voltage of each knock sensor's signal. If the knock sensor system is operating normally, the PCM should monitor KS signal voltage varying over 0.5 volt above and below the calculated average voltage.


DIAGNOSIS
The PCM calculates an average voltage of each knock sensor's signals and takes instantaneous signal voltage readings. The PCM uses the instantaneous signal voltage readings 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 will set.
^ DTCs P0327 and P0332 are designed to diagnose the knock sensors, 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 P0327 or P0332 to diagnose the Detonation/Spark Knock Symptom. Testing and Inspection