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.
Operation
The KS system has two major components:
The PCM contains a replaceable Knock Sensor (KS) module. The KS module
contains the circuitry that allows the PCM to diagnose the knock sensors and
circuitry
The knock sensor(s) detect abnormal vibration (spark knocking) in the
engine. The knock sensor(s) are mounted in the engine block near the cylinders.
The knock sensor(s) produce an AC output voltage which increases in amplitude
and frequency with increased severity of detonation. This signal voltage is
input to the PCM. The PCM then adjusts the Ignition Control (IC) timing to
reduce spark knock. The knock sensors are used to detect engine detonation,
allowing the PCM to retard Ignition Control (IC) spark timing based on the
KS signal being received.
Diagnosis
If the KS module is missing or faulty causing a continuous knock condition
to be indicated, the PCM will set DTC P0325.
The scan tool has four data display parameters available for diagnosing
the KS system. The four parameters are described as follows:
| • | KS Activity is used to monitor the input signal from the knock
sensor. This parameter will display Yes while detonation is being detected. |
| • | Knock Retard is the indication of how much the PCM is retarding
the spark. The PCM will retard spark in response to any of the following conditions: |
| - | An active knock sensor system DTC is set. |
| - | The knock sensor signal is indicating detonation. |
| - | The traction control system desired torque signal is indicating
a traction control event. |
| • | KS Minimum Learned Noise indicates the minimum level that the
PCM has detected on the noise channel while the noise level was being learned.
The PCM uses this parameter for diagnosis of the KS system. If the PCM determines
that an abnormally high learned minimum or maximum noise level is being experienced,
a DTC P0326 will set. |
| • | KS Noise Channel indicates the current voltage level being monitored
on the noise channel. The PCM monitors the noise channel level to ensure that
the KS sensors, the KS module, and the related wiring is operating correctly.
If the voltage level on the KS noise channel circuit is below the range considered
normal, DTC P0327 will set, indicating a fault in the KS circuit or one of
the knock sensors. |
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. However, if no DTC was set but the KS system is suspect
because detonation was the customer's complaint, refer to Detonation/Spark
Knock in Symptoms.
