Under the intake manifold is where the starter lies, which together with the engine bell housing links to it. Large wire (X6512 or B-t- connector) for direct battery voltage transmission and smaller wire (X6510), that makes the starter solenoid to operate via ignition switch and car access system (CAS) are main components of starter wiring. In case the battery state of charge is good and a vehicle fails to start, then there is a need to check whether the solenoid clicks repeatedly. Also examine cables between the battery and starter as well as terminals and ground connections so as to ensure they are in good contact including special attention given on ground connections among the body, battery as well as engine. If it does not appear any fault, probably your starter is bad and needs replacement with a new one. Should you experience this condition; test CAS module if possible through using BMW scant tool that facilitates such tests; however if it's not feasible try another way like ensuring clutch switch module set up properly thus pressing it against floor entirely and still if this doesn't work replace neutral safety switch located at transmission mechatronics electronics because when it breaks down no-start issue occurs consequently. The location of the starter under an intake manifold makes its accessibility difficult but in case of possibility, one can take readings from 12.6-volt battery terminal (B+) along with terminal X6510 at starting motor while ignition should be in start position by using a voltmeter for instance . If there is no voltage presence between CAS and starting terminal then check wiring along with CAS especially other inputs interfering with power supply at solenoids level. On other side of visible wiring defects are present plus voltage too exists, your problem most likely comes out from your malfunctioning starting motor.
