Knock Sensors
| ITEM | DESCRIPTION |
|---|---|
| 1 | Knock sensor - Front |
| 2 | Knock sensor - Center |
| 3 | Knock sensor - Rear |
The knock sensors are piezo-ceramic sensors that allow the PCM to employ active knock control and prevent engine damage from pre-ignition or detonation.
Each knock sensor is secured with a single screw. On each knock sensor, a 2-pin connector provides the interface with the engine harness.
The PCM compares the signals from the knock sensors with preset tables in its memory to determine when detonation occurs. When detonation is detected, the PCM retards the ignition timing on that cylinder 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 avoids engine damage if low quality fuel is used. The Malfunction Indicator Lamp (MIL) gets illuminated, although the driver may notice that the engine 'knocks' in some driving conditions. The 'knocks' result in a decrease in engine performance and smoothness.
The PCM uses a default stored value if a sensor fails.