I am driving BMW 530d 2006 model car. After driving some kilometers and stopping the car, when I try to start again, the car doesn't start. It will start after 10 to 12 hours of resting. Please help me.
This may be related to the coolant temperature sensor. When the car is warm, if the coolant temperature sensor is broken, it might indicate the engine is cold, and then the ECU tries to start a warm engine like it would start a cold engine.
After 10 to 12 hours of rest, the engine has become cold again, and now the procedure to start it like a cold engine works well.
Of course, your battery and/or alternator might be dying, and the 10 to 12 hours of rest may be enough for the battery to be able to provide some juice for starting the car.
Does the starter motor crank well in the no-start condition? If it is cranking well, the problem is probably the coolant temperature sensor, and if not cranking well, the problem may be in the alternator and/or battery.
Do note that there may be multiple coolant temperature sensors. Some control the radiator fan, some display the temperature on the dashboard, and some feed the ECU with coolant temperature information. The one that feeds the ECU with coolant temperature information is the relevant one here.