BMW 318/325/M3/525/535/M5 1989-1993 Repair Information

Knock Sensor


The knock sensors provide information to the DME to determine whether knocking is taking place. The sensors are mounted to the engine block under the intake manifold. The sensor are used on M42 engines.


  1. Turn the ignition switch OFF .
  3. Disconnect the injector plug plate from the injectors and place to the side.
  5. Remove the upper intake manifold and disconnect the wire duct from the lower intake manifold.
  7. The knock sensors are plugged into the holder with the upper plug for cylinder 1 and 2 knock sensor. The lower plug is for cylinder 3 and 4 knock sensor. Mark the locations of the plugs and disconnect.
  9. Note the routing of the leads and the angle the sensors are mounted. Disconnect the water pipe crossing past the knock sensors. Remove the sensors from the engine block.

To install:
  1. Install the cylinder 1 and 2 knock sensor with the lead pointing toward the back of the engine. The lead should make a 70 degree angle from vertical to avoid interference with other engine components.
  3. Install the cylinder 3 and 4 knock sensor with the lead point to the front of the engine, parallel with the centerline of the crankshaft.
  5. Install the water pipe and connect the knock sensor plugs. Install the wire duct and upper intake manifold. Install the injector plug plate.