Circuit Description
WARNING: This page is about a different car, the 2003 Toyota Sequoia. However, it is still accessible from the selected car via links, so may be relevant.
The knock sensors are fitted on the right bank and left bank of the cylinder block to detect the engine knocking. Each sensor contains a piezoelectric element which generates voltage when it becomes deformed, which occurs when the cylinder block vibrates due to the knocking. If the engine knocking occurs, the ignition timing is retarded to suppress it.