Knock Sensor: Description and Operation

PURPOSE
When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount.

OPERATION
The knock sensor threads into the side of the cylinder block in front of the starter motor.

Knock sensors contain a piezoelectric material which constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates.
- As the intensity of the crystal's vibrations increase, the knock sensor output voltage also increases.

CAUTION: Over or under tightening effects knock sensor performance -- possibly causing improper spark control.

CIRCUIT OPERATION
The knock sensor provides an input to the Power- train Control Module (PCM) on circuit K42. Circuit K42 connects to cavity 24 of the PCM.

The PCM provides ground for the knock sensor signal (circuit K42) through circuit K4. Circuit K4 connects to cavity 43 of the PCM connector.

Helpful Information
Circuit K4 also splices to supply ground for the signals from the following:
- Upstream heated oxygen sensor
- Downstream heated oxygen sensor
- Camshaft position sensor
- Crankshaft position sensor
- Engine coolant temperature sensor
- Throttle position sensor
- Intake air temperature sensor
- Manifold absolute pressure sensor
- Vehicle speed sensor