BMW Alternator & BMW Starter Motor Fault Diagnosis 

If  your  starter motor  is  turning  very  slowly  and your interior lights are dull then you may have a

faulty battery or the battery may be weak. To  check  this  it  is  advised  to  take your battery to an auto electrician who can check it.

If you turn the ignition switch & nothing happens at all then you may want to check the connections

from your battery to your BMW starter motor.  These sometimes get rusty and need cleaning.

If  you  turn  the  ignition  and  hear  a  clicking  noise  then  your starter motor gear may be sticking.

Put your car into 4th or 5th gear, make sure your handbrake is off and  gently push your car forwards  and backwards. This sometimes  releases the gear  in  the starter motor and lets you start the car as normal. The BMW starter motor gear will nead replacing at some point.

If your battery is not charging then you  may have a loose alternator belt.  If you hear  a screeching noise then tighten your belt and then the alternator will charge your battery.

You can test if your  BMW alternator  is   charging  correctly  by  using  a  multimeter.  Set  the meter to DC current and connect to the battery  terminals.  Turn  off   all   lights  and  interior  electrics and rev the car  to  2500rpm.  The  multimeter  should  read between  13.5  and 14.4 volts. The  BMW alternator needs to supply more voltage than the rated 12v battery.

Remember if in doubt about your BMW starter motor or BMW alternator then  take your vehicle to a reputable auto electrician who can diagnose any faults.