2006-2008 Polaris Snowmobiles FS/FST Service Manual., Page 90Get this manual
EFIIgnition Systems Knock Sensor Circuit (FST Only)
The knock sensor is piezoceramic type sensor that transforms the internal engine acoustic information into an electrical signalThe ECU uses this information to determine the level of combustion knock inside each cylinderThe knock sensor is located on the intake-side of the engine underneath the water outlet manifold