Power and Ground Distribution: Description and Operation

Vehicle System Voltage Supply

Vehicle system voltage supply
Due to the steady increase in the number of electrical functions in the areas of comfort, communication and safety in vehicles, the voltage supply is becoming ever more significant. Two independent power distribution boxes are installed. The front power distribution box is located in the vicinity of the glove box; the rear power distribution box is on the right side of the luggage compartment.







Brief component description
The following components for voltage supply are described:
- Battery
- Intelligent battery sensor
- Alternator
- Fuse block on the battery
- Power distribution box, rear
- Power distribution box at front in the junction box
- Power distribution box in the engine compartment and electronics box
- Battery cables
- Car Access System (CAS)
- Junction box electronics (JBE)

System wiring diagram







Battery
The vehicle battery is fitted in the centre at the rear of the luggage compartment floor. An AGM battery is always fitted. The AGM battery has a capacity of 90 Ah. The AGM battery provides above all the advantage of higher cycle resistance.







IBS: Intelligent battery sensor
The intelligent battery sensor (IBS) is a mechatronic component with its own micro-controller for monitoring the battery condition. The IBS continuously measures the following values on the battery:
- Voltage
- Charge and discharge current
- Battery temperature







For data transfer, the IBS is connected to the DME (Digital Motor Electronics) or DDE (Digital Diesel Electronics) via a local interconnect network bus (LIN bus).

Alternator
With the engine running, the alternator generates a variable charging voltage for battery charging. The variable charging voltage is influenced by the power management depending on the temperature and current by the DME/DDE raising the engine speed.

Fuse block on the battery
The fuse block can only be completely replaced. Fuses cannot be replaced individually.
The fuse block contains fuses for the following consumer units:
- Power distribution box at front in the junction box
- Power distribution box, rear
- Electromechanical power steering (EPS) without integral active steering (SA 2VH) or with 24 V (connection to the cut-off relay and auxiliary battery), auxiliary engine starting equipment (hybrid car).
- DC/DC converter (400 W) for support during engine start (vehicle with automatic engine start-stop function)
- Power distribution box in the engine compartment for electric auxiliary heater or electric fan (850 W or 1000 W)
- Valvetronic, common rail (fuel injection for diesel), electric coolant pump (100 A)
- Rear axle slip angle control
- Intelligent battery sensor IBS







Power distribution box, rear
The rear power distribution box is located in the luggage compartment on the right. Alongside the fuses, a number of relays are also plugged into or soldered onto the printed circuit board. If one of the soldered relays is faulty, the complete power distribution box must be replaced.







Power distribution box at front in the junction box
The front power distribution box is located below the dashboard on the right side, behind the glove box. There is an internal plug connection for the junction box electronics (JBE) in the right area of the power distribution box. When assembled, the front power distribution box and JBE are one unit: junction box. The components power distribution box and JBE are to be replaced individually.







There are a number of relays in the front power distribution box. The relay for terminal. 30B is plugged; the others are soldered onto the printed circuit board:
- Bi-stable relay terminal 30F
- Relay terminal 15N
- Relay for headlight cleaning system
- Relay for the rear wiper
- Fanfare horn relay

Power distribution box in the engine compartment
The purpose of the power distribution box in the engine compartment is to provide the voltage supply for the electric auxiliary heater and electric fan. The Valvetronic, common rail (fuel injection for diesel) and electric coolant pump (100 A) are supplied via the electronics box.

Battery cable
Three battery cables run along the vehicle underbody from the fuse block on the battery and right to the engine compartment:
- One of the battery cables leads across the positive battery connection point to the starter motor and to the alternator. This battery cable is monitored by the crash safety module.
- One cable supplies the engine electronics (electronics box) with voltage.
- One cable leads to the power distribution box in the engine compartment.
Depending on the version, different line cross-sections are used.

Car Access System (CAS)
The CAS is involved in terminal control (terminal R, terminal 15, terminal 15N and terminal 30B). The terminal control supplies important messages for the voltage supply. The CAS controls the relays for terminal 30B and terminal 15N. The CAS is a bus user of K-CAN2.

Junction box electronics (JBE)
The junction box electronics control the bi-stable relay of terminal 30F at the request of the following components:
- Central gateway module for inhibited sleeping or unauthorized waking.
- Intelligent battery sensor for standby current violation or reaching the startability limit.

System functions
The following system function for voltage supply is described:
- Terminal control (terminal 15N, terminal 30B and terminal 30F)



Terminal control (terminal 15N, terminal 30B and terminal 30F)
Terminal 15N, terminal 30B and terminal 30F are switched terminals that provide the voltage supply for control units and components in the vehicle electrical system. The switched terminals enable optimization of the energy consumption in normal operation, in the stationary mode (standby current) or in the event of faults.

Terminal 15N
Terminal 15N is used for the voltage supply of control units and components that are required for "Ignition on". Terminal 15N is activated together with the logical terminal 15 by activating the start/stop button. Terminal 15N is switched off with an after-running period of 5 s after switching off the logical terminal 15.

Terminal 30B
Terminal 30B provides the voltage supply for control units and components that in normal operation are required when the driver is present. Terminal 30B is controlled by the CAS. Terminal 30B is activated in the following events:
- Unlocking, locking or deadlocking the vehicle.
- Changing a door contact (driver's side front or rear, front passenger side front or rear).
- Changing the rear lid contact switch or actuating the rear lid button.
- Operating the START-STOP button.
- Request from the Telematic Control Unit (TCU).

Terminal 30B is switched off with an after-running period that depends on the state:

State After-running period
Unlocked vehicle or opened 30 min
tailgate.
For vehicles from I level 03/2010 12 min
and without any of the following
optional equipment: 633, 639,
644, 6VC or 6NB.
After waking by the TCU 3 min
Deadlocked vehicle and closed 1 min
tailgate
Reaching the startability limit 1 min
After sending the 'power-down' 10 s
command

The after-running period of terminal. 30B can be extended at the request of auxiliary consumer units. Auxiliary consumer units are for example the independent ventilation or auxiliary heater function, TCU and electric fan.

Terminal 30F
Terminal 30F provides the voltage supply for control units and components that in the normal operation require continuous positive but can be switched off in the event of faults. Terminal 30F is controlled by the JBE. In the event of a fault, a reset of terminal 30F is carried out first. If the fault persists, this is followed by a shutdown. The following faults lead to a reset or shutdown of terminal 30F:
- Prevents sleeping after terminal 30B OFF
- Unauthorized waking after terminal 30B OFF
- Standby current violation
- Reaching the startability limit
Terminal 30F is reactivated together with terminal 30B.

Notes for Service department

General notes

NOTE: Charging and trickle charging of the battery.

The battery may only be charged using the chargers approved by BMW Group at a constant charging voltage of 14.8 V.If possible, the battery temperature during charging should be between 15 deg C and 25 deg C. Under these conditions, the battery is adequately charged when the charge current drops below 2.5 amps. If the battery is recharged at low temperatures, the charging procedure should not be ended until the charge current drops below 1.5 A. If the battery is to be recharged while it is still installed, it must be recharged using the jump start terminal points. Only then can you be sure that recharging is correctly recognized by the vehicle electronics on vehicles with an intelligent battery sensor (IBS). If the battery is charged directly at the battery terminals, this could lead to a misinterpretation of the battery condition and even unwanted Check Control messages or fault entries. The cigarette lighter is supplied by the front power distribution box via the switched terminal 30B. After terminal 30B off, the relay de-energizes. This means that a trickle charger connected at the cigarette lighter would be disconnected from the battery. Only charge the battery via the jump start terminal point.

Diagnosis instruction

Energy diagnosis
A breakdown due to a flat battery or problems in the vehicle electrical system can have wide variety of causes. In most cases, the cause does not lie with the battery itself. For this reason, replacing the battery will only rarely provide a sustained solution to the problem. Instead, systematic diagnosis of the source of the fault is needed. Faults are often no longer present when the vehicle comes to the workshop. This is why data stored in the vehicle is the basis for diagnosis. Information on the battery condition as well as functional processes in the various bus systems are stored in the corresponding control units. This information can be called up and evaluated by the BMW diagnosis system. The BMW diagnosis system has a procedure for this. The testing procedure for energy diagnosis reads all the relevant data from the corresponding control units.

NOTE: Register battery replacement.

After installing a new battery, the service function 'Register battery replacement' should be run. The battery replacement has to be registered in order to tell the power management system that a new battery has been installed in the vehicle. If the battery replacement is not registered, the power management will not function properly, with the result that Check Control messages may be displayed and functions limited by individual electrical consumers being switched off or having their power consumption reduced, for example.

Notes on encoding/programming
The battery type and battery capacity are coded in the Car Access System (CAS). The data can be read out using the BMW diagnosis system.

No liability can be accepted for printing or other faults. Subject to changes of a technical nature