Knock Sensor System Description (LDD or LUJ)
Circuit/System Description
The knock sensor system enables the engine control module (ECM)
to control the ignition timing for the best possible performance
while protecting the engine from potentially damaging levels of
detonation. The ECM uses the knock sensor system to test for
abnormal engine noise that may indicate detonation, also known as
spark knock.
Sensor Description
This knock sensor system uses one or two flat response dual-wire
sensors. The sensor uses piezo-electric crystal technology that
produces an alternating current (AC) voltage signal of varying
amplitude and frequency based on the engine vibration or noise
level. The amplitude and frequency are dependant upon the level of
knock that the knock sensor detects. The ECM receives the knock
sensor signal through 2 isolated signal circuits.
If the ECM has determined that knock is present, it will retard
the ignition timing to attempt to reduce the knock. The ECM is
capable of controlling spark retard on an individual cylinder
basis. The ECM will always try to work back to a zero compensation
level, or no spark retard. knock sensor diagnostics are calibrated
to detect faults with the knock sensor circuitry inside the ECM,
the knock sensor wiring, or the knock sensor voltage output. Some
diagnostics are also calibrated to detect constant noise from an
outside influence such as a loose/damaged component or excessive
mechanical engine noise.
|