Brief description of components

The following components are involved in the power supply:

• Alternator 

  The alternator generates the charge voltage for the battery and the power supply for the consumers. The alternator generates a variable voltage, depending on the engine speed (alternator voltage).

  The power management system regulates this variable voltage.

• Battery 

  The vehicle battery is fitted inside a plastic casing in the luggage compartment. The capacity of the battery installed depends on the engine used and the equipment installed in the vehicle.

• Junction box 

  The junction box is fitted behind the glove box underneath the instrument panel.

  The junction box consists of a power distributor and a control unit, the junction box electronics (JBE, see below).

  The power distributor holds fuses and relays. The following relays are of particular importance for the power supply:

  • Terminal 15 relay
  • Terminal 30g relay for consumer cutoff (see below under "SYSTEM FUNCTIONS ")
  • Terminal 30g-f relay for cutoff in case of fault (see below under "SYSTEM FUNCTIONS ")
  NOTE: For current details about the pin assignment and fuse assignment of the junction box electronics and the power distributor, please refer to appropriate WIRING DIAGRAMS article.
  Different versions of the power distributor are fitted, depending on the model series and Model Year measures.
  For example, the complete fuse assignment may change as part of Model Year measures.

  • 03/2007 Model Year change:

    primarily changes to pin assignment

  • 09/2007 Model Year change:

    primarily changes to fuse assignment

  
  Depending on the vehicle equipment, various relays are mounted on the boards in the power distributor.
• Front and rear power distributors 

  The BMW 1-Series and the BMW 3-Series have the following power distributors:

  1. Power distributor in the engine compartment: Electronics box
  2. Power distributor in the luggage compartment: Rear fuse block

  The fuse block is secured to the vehicle battery by a retaining clip.

  The fuse block can only be replaced as a complete unit. Fuses cannot  be replaced individually.

  The fuse block holds the fuses for the following consumers:

  • Valvetronic
  • Common rail (fuel injection on diesel)
  • Electric auxiliary heater
  • Power distributor in junction box
• Intelligent battery sensor 
  • Only on vehicles with High equipment level, e.g. CCC or M-ASK (CCC: Car Communication Computer, M-ASK: Multiaudio system controller)

  The intelligent battery sensor evaluates the current quality of the battery. The intelligent battery sensor is a part of the battery negative terminal.

  The intelligent battery sensor regularly (cyclically) measures the following values:

  • Battery voltage
  • Charge current
  • Discharge current
  • Battery temperature

  The following control units are involved in the power supply:

• JBE: Junction box electronics 

  The JBE is the control unit in the junction box.

  The JBE is the central data interface in the vehicle (gateway for the bus systems).

• CAS: Car Access System 

  The Car Access System is involved in the terminal control (terminal R, terminal 15, terminal 30g).

  The terminal control supplies important messages for the power supply.

  The CAS is connected to the following components and control units:

  • The Car Access System is connected by a direct wire to the START/STOP button and to the slot for the ID transmitter.

    The START/STOP button and the slot are located next to the steering column.

  • The starter motor and the DME/DDE are connected to the CAS.

  The CAS control unit is a bus subscriber on the K-CAN.

• DME: Digital engine electronics or 

  DDE: Digital diesel electronics 

  The DME/DDE influences the power supply as follows: If the alternator voltage drops, the DME/DDE will increase the engine speed as needed.

  The software for this is called "power management".

  The DME/DDE is connected to the PT-CAN (Powertrain Controller Area Network) as part of the bus system.

  If an intelligent battery sensor is fitted, the DME/DDE will evaluate the current battery condition. In this way, the DME/DDE also influences terminal 30g-f (see below under "SYSTEM FUNCTIONS ").

• MRS: Multiple restraint system 

  The MRS control unit interrupts the power supply as follows if an accident exceeding a certain severity occurs:

  • The safety battery terminal is separated from the battery.
  • The electric fuel pump is switched off.

  The following data buses and wires are important for the power supply:

• Bitserial data interface 

  The bitserial data interface is the data connection between the engine control unit (DME/DDE) and the alternator.

• 2 battery cables 
  1. 2 battery cables connect the battery to the engine compartment:
  • One of the battery cables runs via the jump-start connection point to the starter and alternator.
  • The other cable is used for the voltage supply for the fuel injection system (on spark-ignition engines: Valvetronic, on diesel engines: Common rail system).

  Both battery cables are routed on the vehicle underbody on the BMW 1-Series and BMW 3-Series.