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
- Electronics box in engine compartment
- Capacitor box
- Battery cables
- DC/DC converter for support when starting the engine (only with automatic engine start-stop function)
- 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 capacity of the AGM battery depends on the vehicle type and the vehicle equipment: 80 Ah, 90 Ah or 105 Ah.
The AGM battery primarily offers the advantage of greater rechargeability.
Battery type and battery capacity
When replacing an AGM battery, the replacement must always have the same or higher battery capacity.
IBS: Intelligent battery sensor
The intelligent battery sensor (IBS) is a mechatronic component with its own microcontroller 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).
The intelligent battery sensor installed enables better determination of the battery condition: Identification of faulty battery cells, determining remaining battery capacity.
Refer to following functional description: Battery and IBS.
Alternator
With the engine running, the alternator generates a variable charging voltage for battery charge. 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 renewed. Fuses cannot be renewed individually.
The fuse block contains fuses for the following consumer units:
- Power distribution box at front in the junction box
- Power distribution box, rear
- Electronics box in engine compartment for Valvetronic, common rail (fuel injection for diesel fuel)
- Top HiFi amplifier
- 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 power distribution box and junction box electronics components must each be renewed.
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
Electronics box in engine compartment
The power distribution box in the engine compartment provides a voltage supply to the Valvetronic, common rail (fuel injection for diesel fuel) and electric coolant pump.
Capacitor box
The voltage supply for the following components is provided by a front power distribution box , which is connected to the positive battery connection point:
- Electric auxiliary heater
- Electric fan (400 W, 600 W and 850 W)
- Electromechanical Power Steering (EPS)
- Return pump (Dynamic Stability Control)
To reduce the ripple in vehicle voltage caused by the alternator, an ignition capacitor is installed in the power distribution box. Capacitor, fuses and power distribution box together form the capacitor box.
Battery cable
Three battery cables run along the vehicle underbody from the fuse block on the battery to the engine compartment:
- One of the battery cables leads to the capacitor box and on to the starter motor and alternator via the positive battery connection point. This battery cable is monitored by the crash safety module.
- One cable leads to the power distribution box in the engine compartment.
DC/DC converter for providing support during an engine start
Depending on equipment levels, vehicles with automatic engine start-stop function (MSA) may have one or two DC/DC converter installed to support the voltage supply when starting the engine. Both DC/DC converter (180 W) are installed in the rear luggage compartment floor.
The following components are supported by the DC/DC converter when the engine is started:
- Headunit
- Central Information Display (CID)
- Combox
- Top HiFi amplifier
- Dynamic Stability Control
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)
See also the following functional descriptions: Power management, Battery and IBS.
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 tailgate contact switch or operating the tailgate button.
- Changing the rear window contact switch or operating the rear window button.
- Changing the engine compartment lid contact switch.
- Operating the START STOP button.
- Combox request.
Terminal 30B is switched off with an after-running period that depends on the state:
Condition After-running period
Unlocked vehicle or opened 12 min 30 min
tailgate. For vehicles with the
following optional equipment:
633, 639, 644, 6VC or 6NB.
After wake up by the 3 mins.
Combox
Deadlocked vehicle and closed 3 mins.
tailgate
Reaching the startability 3 mins.
limit
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. The number of extensions to the terminal 30B after-running period and the maximum duration of the terminal 30B after-running period is determined for each auxiliary consumer:
Terminal 30F
Terminal 30F provides the voltage supply for control units and components that in the normal operation require the terminal 30 but can be switched off in the event of faults. Terminal 30F is controlled by the junction box electronics.
In the event of a fault, terminal 30F is reset. If the fault persists, this is followed by a shutdown. Terminal 30F is automatically switched off in case of an immobilization period for 22 days in order to reduce the standby current and ensure that the vehicle starting capability lasts for longer.
The following faults lead to a reset or shutdown of terminal 30F:
- Go to sleep prevented after terminal 30B OFF.
- Unauthorized wake up after terminal 30B OFF
- Standby current violation.
- Startability limit reached.
Terminal 30F is not reset or switched off in the following circumstances:
- Terminal 30B ON
- Parking light, side lights or hazard warning flashers ON.
- Power window relay fault detected.
Terminal 30F is reactivated together with terminal 30B.
Notes for Service department
General notes
NOTICE: Charging and trickle charging of the battery.
The battery may only be recharged using a BMW Group-approved charger at a constant charging voltage of 14.8 V. If possible, the battery temperature should be between 15 °C and 25 °C during charging. Under these preconditions, 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 charged while it is still installed, it must be charges using the jump start terminal points. Only then can you be sure that charging 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, fault entries or functional limitations. The cigarette lighter gets his voltage supply 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, battery replacement will only rarely provide a sustained solution to the problem. Instead, systematic diagnosis of the source of 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 fault 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 procedure for energy diagnosis reads all the relevant data from the corresponding control units.
NOTICE: 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.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.