In order to service or repair the engine, one way is to remove the DME main relay that is situated in the electronics box located at the right rear of the engine compartment. Care should be taken when identifying relays since their locations can differ. If you connect test equipment that supplies 12 volts on terminal 15(+) of ignition coil or spark plug coil wires are removed for disabling ignition, it may cause damage to ECM. The ignition system wires, multiple wire connectors and equipment leads should only be connected or disconnected with the ignition off. Never disconnect a battery while an engine is running and ensure that you read through precautions before removing battery cables. After turning OFF the ignition switch, it is recommended to wait for at least 1 minute before disconnecting ECM connector because there might be some kind of damage possible on control module if this timing isn't followed strictly. Electrical tests should be conducted by using digital multimeter while quick tests can be made by using LED test light. Aluminum fasteners must not replace steel bolts in order to prevent electrochemical corrosion of aluminum-magnesium alloyed components of an engine. Every time aluminum fasteners come loose, they must be thrown away and instructions regarding torque specifications including angle specification must also be followed during installation of aluminum fasteners. BMW X3 models have digital motor electronics (DME), also called Motronic ECM which controls fuel injection and ignition as one integrated unit on these engines.BMW X3 engines have individually controlled/monitored coils on them and therefore servicing them requires cleanliness so that ignitions coils do not fail.Accordingly, ECM uses different inputs such as coolant temperature; knock detection; engine load; intake air temperature; knock detection in adjusting its timing.Likewise crankshaft sensor detects crankshaft position and speed rotation while camshaft sensors respond to impulse wheels mounted on camshafts' ends for various functionalities such as cylinder recognition, spark timing, sequential fuel injection, VANOS (camshaft timing) and Valvetronic (variable valve) control. Knock sensors can retard ignition spark when knock is detected in the combustion chambers that may damage an engine; they are located at the left side of the cylinder block beneath an intake manifold, both should be replaced if a single fault occurs.
