A knock sensor is installed on both 2.0L SPI engines and 20LZetec-E engines. On Zetec-E engines, it's bolted to the firewall-side of the cylinder block, just ahead of the starter motor, On SPI engines, it is located on the front side of the block, just below the exhaust manifold,On 2.3L and 2005 and later 2.0L engines, it is located on the block,under the intake manifold. The knock sensor wiring plug is clipped to a bracket next to the engine oil dipstick. Slide the wiring plug downward to remove it from the clip, then separate the two halves of the wiring plug. Trace the wiring down to the knock sensor, then unscrew the center bolt and remove the sensor from the engine. On 2.3L and 2005 and later 2.0L engines, the intake manifold must be removed first. Installation is a reversal of removal, noting the following points: Clean the sensor and its location on the engine. The sensor must be positioned so that it does not contact the cylinder head,or the crankcase ventilation system oil separator housing (where applicable). The sensor bolt must be tightened to the specified torque, as this is critical to the sensor's correct operation.