Knock Sensor
The knock sensors are piezo-ceramic sensors. The knock sensors allow the PCM to employ active knock control and prevent engine damage from pre-ignition or detonation.
There are knock sensors located on the inboard side of each cylinder head. There are 2 mid-way between the front 2 cylinders and 2 mid-way between the rear 2 cylinders. Each knock sensor is installed with 1 screw. On each knock sensor, a 2-pin electrical connector provides the interface with the engine wiring harness.
The PCM compares the signals from the knock sensors with mapped values stored in memory to determine when detonation occurs on individual cylinders. When the PCM detects a detonation it retards the ignition timing on that cylinder for a number of engine cycles. The PCM then gradually returns it to the original setting.
The PCM cancels closed loop control of the ignition system if the signal received from a knock sensor becomes implausible. In these circumstances the PCM defaults to base mapping for the ignition timing. This makes sure that the engine does not become damaged if low quality fuel is used. The MIL does not illuminate, although the driver may notice that the engine 'pinks' in some driving conditions. The vehicle displays a drop in performance and smoothness.
The PCM calculates the default value if 1 sensor fails on each bank of cylinders.