The knock sensor, as the name suggests, detects knock and sends a voltage signal to the ECM. The ECM uses the knock sensor signal to control timing. The engine knock occurs within the particular frequency range. Located in the engine block, cylinder head or intake manifold, the knock sensor is tuned to detect that frequency. Contained inside the knock sensor is a piezoelectric element that generates a voltage when pressure or vibration is applied to them. Each piezoelectric element in the knock sensor is tuned to the engine knock frequency.
To make it further clear, the knock sensor is designed to sense when the fuel burning unevenly and causing irregular vibrations in the engine. Generally, it consists of an electric coil that is wound around two ceramic rods with a magnet in the center. These ceramic rods vibrate when there is an engine vibration which disturbs the coils magnetic field and alters the current passing through the coil. Now, the disturbance returns to the computer as a signal pattern that can be analized by the computer. The computer then determines whether the vibrations are characteristic of engine knocking.
In your Saab vehicle, the Saab knock sensor is considered to be the heart of the engine management system. This enables your Saab to obtain the optimum combination of fuel/air mixture and timing to add up power and efficiency generated. The goal here is actually to waste lesser amount of gas and save more bucks. Note that an engine knock can be caused by using lower octane gas than what is recommended by the manufacturer or by over advanced ignition timing.
Another probable cause is the so called "hot spot" in the combustion chamber. The carbon that has accumulated in the combustion chamber can glow red during high engine load. This will now cause the air/fuel mixture to ignite prematurely. In other words a "pre-ignition" can happen and this is the counterpart of taking a very large hammer and hitting the piston before it rises to the top.
Your knock sensor must be reliable and not faulty as this will degrade the vehicle performance and fuel economy. Worse, this can cause engine damage leading to the occurrence of more malfunctions. A good knock sensor has no corroded terminal and damaged wires. Here at Parts Train, you can find knock sensors for Saab and other makes should you need to replace your stock Saab knock sensor. Shop with us today and we will let you know what customer satisfaction is really all about.