Jeep Workshop Manuals
Grand Cherokee 2WD V6-3.7L (2008)
Sensors and Switches > Sensors and Switches - Powertrain Management > Sensors and Switches - Computers and Control Systems > Knock Sensor > Component Information > Description and Operation > Description > Page 1408
Knock Sensor: Description and Operation
Two knock sensors are used; one for each cylinder bank. When the knock sensor detects a knock in one of the cylinders on the corresponding bank, it
Knock sensors contain a piezoelectric material which constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As
The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives the knock sensor voltage signal as an
The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, knock retard is allowed.
Knock retard uses its own short term and long term memory program.
Long term memory stores previous detonation information in its battery-backed RAM. The maximum authority that long term memory has over timing
Short term memory is allowed to retard timing up to a preset amount under all operating conditions (as long as rpm is above the minimum rpm) except at
NOTE: Over or under tightening the sensor mounting bolts will affect knock sensor performance, possibly causing improper spark control.
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