For many components, it is important that the ECM hnow the position and/or mode of the compoment. A switch is used as a sensor to indicate a position or mode. The switch may be on the supply side or the ground side of a circuit
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Knock Sensor
The Knock Sensor detects engine knock and sends a voltage signal to the ECM The ECM uses the Knock Sensor signal to control timing
Engine knock occurs within a specific frequency range The Knock Sensor, located in the
engine block, cylinder head, or intake manifold is tuned to detect that frequency
Knock Sensor Location
Knock Sensor
To ECM
Fig, 2-87
Inside the knock sensor is a piezoelectric element Piezoelectric elements generate a voltage when pressure or a vibration is applied to them The piezoelectric element in the knock sensor
is tuned to the engine knock frequency
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Piezoelectric
Fig 2-88
Element
78526113
Voltage Generation
When knock occurs, the voltage output increases
Fig 2-89
T852f114
Fig 2-90
18521115
Voltage
The vibrations from engine knocking vibrate the piezoelectric element generating a voltage The
voltage output from the Knock Sensor is highest at this time
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1 What is the purpose or function of a Knock Sensor?
2 Explain how the PCM (ECM) uses the Knock sensor input signal?
3 Where are Knock sensors usually located?
4 Explain the construction of a Knock Sensor?
5 Draw a scope pattern of a Knock Sensor?
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