Refer to Electronic Engine Controls in Section 4 for information on servicing the Knock Sensor (KS).
The Knock Sensor (KS) provides information to the Engine Control Module (ECM) to determine whether detonation is taking place. If knock is detected the ECM will retard the ignition timing until the knock is eliminated. This prevents the engine from doing internal mechanical damage that can occur when detonation is present. The KS sensor also allows the ECM to adapt and optimize the ignition timing based on engine load, throttle position and the quality of the fuel being used. If a low grade of fuel is selected, the ECM will allow for safe operation of the engine, however the engine's power output will be compromised to allow for safe operation on the low grade of fuel.
To optimize the engine's performance, a quality grade of fuel should be used as outlined in the owner's manual and on labels installed in the fuel filler area.
The Knock Sensors were first used on the M42 engines and are found on all 3 series and Z3 engines that are OBD II compatible. The sensors are mounted to the engine block under the intake manifold.
Removal & Installation
The KS sensors are located on the left side of the engine block near the center point of the cylinders.
- Turn the ignition switch OFF .
- Disconnect the injector plug plate from the injectors and place to the side.
- Remove the upper intake manifold and disconnect the wire duct from the lower intake manifold.
- 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.
- 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.
- 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.
- 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.
- Tighten the Knock Sensor (KS) to 15 ft. lbs. (20 Nm).
- Install the water pipe and connect the knock sensor plugs. Install the wire duct and upper intake manifold. Install the injector plug plate.
If a Knock Sensor (KS) malfunctions, a Diagnostic Trouble Code (DTC) will be stored in the Engine Control Module (ECM) fault memory. Due to their physical location and the dynamic operation of the KS sensor, diagnosis should be performed using a BMW service tester, or suitable Data Scan Tool (DST) to check for stored faults.