Lumina V6-3.8L VIN K (1998)
Knock Sensor: Description and Operation
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.
To control spark knock, a Knock Sensor (KS) system is used. This system is designed to retard spark timing to reduce spark knock in the engine. This
allows the engine to use maximum spark advance to improve driveability and fuel economy.
COMPONENTS
The KS system has two major components:
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KS module.
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Knock sensor.
OPERATION
The knock sensor detects abnormal vibration (spark knocking) in the engine. The knock sensor is mounted in the engine block near the cylinders and
produce an A/C signal under all engine operating conditions. The PCM contains integrated knock sensor (KS) diagnostic circuitry which uses the
input signals from the knock sensors to detect engine detonation. This allows the PCM to retard Ignition Control (IC) spark timing based on the
amplitude and frequency of the KS signal being received.
DIAGNOSIS
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:
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If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 will set.
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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 table for P0327 and
P0332 to diagnose the Detonation/Spark Knock Symptom. See: Powertrain Management/Computers and Control Systems/Testing and Inspection
