A knock sensor is like a small equipment microphone that is usually attached to the engine block and listens for a couple of things that a engine might do. One thing it listens for is pre-ignition or knocking inside the engine usually caused by a few issues including dirty gas, wrong engine timing low octane fuel, wrong air / fuel mixture, and also by the wrong spark plugs. It also listens for engine run on which happens when the vehicle is turned off, but tries to keep running until it stalls. Once a noise is detected, the knock sensor sends a signal to the cars computer which in turn will retard the timing at 2 degree intervals until it corrects the issue. If the knock sensor fails, it can seriously damage the engine, as continuous pre-ignition could cause melting or fractures in the pistons just to name a few.

Fit for
2005 for BMW 320i 2.2L
2000 for BMW 323Ci 2.5L
1999-2000 for BMW 323i 2.5L
2001-2006 for BMW 325Ci 2.5L
2001-2005 for BMW 325i 2.5L
2001-2005 for BMW 325xi 2.5L
2000 for BMW 328Ci 2.8L
2000 for BMW 328i 2.8L
2001-2006 for BMW 330Ci 3.0L
2001-2005 for BMW 330i 3.0L
2001-2005 for BMW 330xi 3.0L
2001-2005 for BMW 525i 2.5L
1999-2000 for BMW 528i 2.8L
2001-2005 for BMW 530i 3.0L
2004-2006 for BMW X3 2.5L
2004-2006 for BMW X3 3.0L
2001-2006 for BMW X5 3.0L
1999-2002 for BMW Z3 2.5L
1999-2000 for BMW Z3 2.8L
2001-2002 for BMW Z3 3.0L
2003-2005 for BMW Z4 2.5L
2003-2005 for BMW Z4 3.0L