Knock Sensor (KS)

WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Identifying Knock Sensors (KS)

Courtesy of VOLVO CARS OF NORTH AMERICA.

The function of the two knock sensors (KS) is to provide the engine control module (ECM) with signals to determine whether the engine is knocking.

The engine control module (ECM) uses the knock sensor (KS) and camshaft position (CMP) sensor signals to identify the cylinder in which knock is present.

The engine management system incorporates two knock sensor (KS), each of which consists of the following components:

housing
sleeve
piezo-electric crystal
contact strips
damping weight
washer
nut

Engine knock produces vibrations which are transmitted through the block. The piezo-electric crystal reacts to these by transmitting a signal (a function of sound wave frequency and amplitude) to the engine control module (ECM).

The front knock sensor (KS) detects knocking in cylinders 1, 2 and 3. The rear knock sensor (KS) detects knocking in cylinders 4 and 5.

The knock sensors (KS) are mounted on the cylinder block.