Knock Sensors

WARNING: This page is about a different car, the 2018 Jaguar XE and 2017 Jaguar XE. However, it is still accessible from the selected car via links, so may be relevant.

The knock sensors are piezo-ceramic sensors that allow the Powertrain Control Module (PCM) to employ active knock control and prevent engine damage from pre-ignition or detonation.

One knock sensor is installed on the inboard side of each cylinder head, adjacent to the air intake for cylinders 3 and 4. Each knock sensor is secured with a single screw. On each knock sensor, a two pin electrical connector provides the interface with the engine 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 detonation is detected, the PCM retards the ignition timing on that cylinder for a number of engine cycles, and 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 ensures the engine will not become damaged if low quality fuel is used. The MIL will not illuminate, although the driver may notice that the engine 'knocks' in some driving conditions and displays a drop in performance and smoothness.

The PCM calculates the default value if a sensor fails on either bank of cylinders.