The knock sensor system enables the PCM to control ignition timing for best performance while protecting the engine from detonation.
The KS system uses one or 2 flat response 2-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The control module receives the KS signal through a signal circuit. The KS ground is supplied by the control module through a low reference circuit. The control module learns a minimum noise level, or background noise, at idle from the KS and uses calibrated values for the rest of the RPM range.
In order to determine which cylinders are knocking, the control module only uses KS signal information when each cylinder is near Top Dead Center (TDC) of the firing stroke. If knock is present, the signal will range outside of the noise channel. If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard.
Removal & Installation
- Raise and safely support the vehicle.
- On 4.3L engines, remove the skid plates if equipped.
- Remove the tire to ease access to the knock sensor.
- If equipped, remove the knock sensor shield.
- Unplug the harness connection from the knock sensor.
- Remove the bolt securing the sensor, then remove it from the engine.
Installation is the reverse of removal. Tighten the bolt to 18 ft. lbs. (25 Nm).
- Connect a digital multimeter to the KS signal circuit and to the KS low reference circuit at the KS.
- Set the multimeter to the 400 mv AC hertz scale and wait for the display to stabilize at 0 Hz.
Tap on the engine block with a non-metallic object near the KS while observing the signal indicated on the multimeter.
NOTEDo not tap on plastic engine components.
- The multimeter should display a fluctuating frequency while tapping on the engine block. If not, replace the sensor.