BMW Battery Terminals explanation: 15, 15N, 15WUP, 30, 30g, 30g_f, 30B, 30F, 50


Oct 18, 2016
2009 E93 335i
So there are a few different power 'terminals' in BMW cars: Terminal 15, Terminal 30g and Terminal 30g_f. However these have received new names as of CAS4 (with Boardnet 2020).

TerminalNew NameDescription
Terminal 0Terminal 0 is a logical terminal and does not provide a power supply. Terminal 0 comprises Terminal 30, Terminal 30B and Terminal 30F.
Terminal 15Terminal 15/Terminal 15NTerminal 15 is used to signal the status “Ignition ON/Ignition OFF” rather than as a power
supply. That applies, for instance, in the case of the digital motor electronics (DME), the
footwell module (FRM) and BMW Night Vision.

Terminal 15 N (Overrun) is used for control units and electrical loads operating at status
“Ignition ON” when the vehicle is being driven. That applies, for instance, to the lane
departure warning (SWW), short range radar (SRR) and Night Vision.
Terminal 15WUPTerminal 15 Wake-up is used to wake up control units that can not be woken up by bus communication.
Terminal 30Control units and components that must continue to function up to the point when the battery is completely discharged are connected directly to the continuous positive, Terminal 30. That relates to units such as the Car Access System 4, roof function center and the junction box module.
Terminal 30gTerminal 30BTerminal 30 Basic is used for control units and electrical loads operating when the driver is present. That applies primarily to components such as the seat module, digital
motor electronics (DME), gearbox control unit (EGS), Controller and CD changer.
Terminal 30g_fTerminal 30FTerminal 30 Fault is used for control units operating in the driver’s absence. That applies, for instance, to the trailer module (AHM), footwell module (FRM), instrument cluster and automatic climate control module (IHKA).
Terminal 50Terminal 50 is provided for controlling the starter motor.
Terminal R

Terminal 30F
Terminal 30F supplies power to control units and electrical devices that are also required when the driver is not present but which can be switched off in the event of a fault. Use: all control units that are not supplied by Terminal 15N or Terminal 30B, are not responsible for vehicle access and do not have to meet a legal requirement for permanent operation. The letter “F” stands for “Fault”.

Terminal 30F is activated by:
• Pressing the buttons on the radio remote control.
• Unlocking/locking/double-locking the vehicle.
• Pressing the START-STOP button.
• Change of door switch status, change of tailgate switch status, change of side-window position.
• Bus message. In the event of a fault (closed-circuit current too high, bus wake-up, sleep-mode inhibitor, start capacity limit reached) Terminal 30F is reset for 10 seconds.

Terminal 30F is not reset or switched off if at least one of the following conditions is met:
• Terminal 30B active.
• Parking lights switched on.
• Side lights switched on.
• Hazard warning lights switched on.
• If an extended overrun time for Terminals 30B and 30F is demanded by a service message from any of a number of control units. Example: when the engine is warm, it can be necessary for the electric fan to run on for up to 11 minutes after the vehicle is parked and locked. In order for the electric fan to be operated, the engine management module must be supplied with power. Since the overrun time in that case is only three minutes (that is currently the short overrun time for Terminal 30B, not one minute), the DME requests the appropriate extension by way of a bus message when the engine is switched off.
• “Sticking relay” detected.

Terminal 30F is switched off if Terminal 30B is off and at least one of the following conditions is met:
• Starting capacity limit reached.
• Another 10 bus wake-ups have occurred after Terminal 30F reset.
• Unexplained bus activity after Terminal 30F reset.
• Violation of closed-circuit current limit detected after Terminal 30F reset.

Terminal 30g
The Terminal 30g Relay prevents increased closed-circuit current consumption by switching off electric loads. The switch-off procedure disconnects various electric loads in a defined manner from the vehicle electrical system. This happens approximately. 60 minutes after terminal R "OFF." The deactivated electric loads are activated again together with terminal 30g "ON." The terminal 30g relay is actuated by the car access system. Power to the following control units is managed by the terminal 30g relay:
• Center console switch center (SZM)
• Rain and low beam sensor (RLS)
• Controller
• Central information display (CID)
• Slide/tilt sunroof (SHD/MDS)
• Satellite radio (SDARS)
• TOP HiFi amplifier
• Telephone
• Head-up display (HUD)
• Active cruise control (ACC)
• Electronic transmission control/SMG
• Dynamic stability control (DSC)
• Adaptive cornering light (AHL)

30g Switch On Conditions
The switch-on conditions for terminal 30g relay are as follows:
• Unlock vehicle or
• Terminal R or
• Status change of door contacts or of trunk contact or
• Telephone wake-up line for telematic services or
• Service applications

30g Switch Off Conditions
The switch-off conditions for terminal 30g relay are as follows:
• 60 minutes after terminal R "OFF" or
• Service applications
• Power Management Switch off

Fault-dependent Shutdown (terminal 30g_f)
The terminal 30g_f relay is controlled by the junction box control unit and switches off the connected electric loads (MASK or CCC) if a fault occurs. The terminal 30g_f relay is a bistable relay. Each switching status is retained even when no power is applied. The terminal 30g_f relay is switched on and off under the following conditions.

Terminal 30g_f ON at:
• Unlock vehicle or
• Terminal R or
• Change in contact status (rear lid and doors)

Terminal 30g_f OFF at:
• Receiving the "Signal OFF" message. Terminal 30g_f relay is switched off after 5 minutes.
• Bus activity for 60 minutes with no switch on condition applicable.
• Vehicle is woken 30 times with no switch on condition applicable.

The terminal 30g_f relay is a bistable relay and is always switched on under normal conditions. It switches off the connected electric loads only in the case of fault. Once the terminal 30g_f relay has been switched off, one of the switch-on conditions is necessary in order to switch it on again.

Terminal 30 Basic
The conditions that result in Terminal 30B being switched on are:
• Requests for ID transmitter e.g. Comfort Access due to request from exterior door handle module.
• Unlocking central locking Locking central locking Double-locking central locking.
• START-STOP button pressed.
• Bus activity e.g. demand for power supply to a part of the electrical system.
• Change of door-switch status Change of tailgate switch status.

Switching Off Terminal 30B
When the vehicle is locked, the Car Access System receives the central double-locking signal. Once the vehicle is locked, Terminal 30B remains on for approx. one minute and is then switched off by the Car Access System. The tailgate must have already been closed. If the vehicle is not locked or if the tailgate remains open, the delay until Terminal 30B is switched off is approx. 30 minutes. After that, the Car Access System switches Terminal 30B off. In addition, Terminal 30B can be switched off when the vehicle is in parked mode if the battery upper starting capacity limit is reached. During fault diagnosis, the power down command can be used to switch off Terminal 30B under defined conditions for the purposes of measuring quiescent current. If the vehicle is in transport mode status, Terminal 30F is switched off.

Terminal 15
After Terminal 30 is switched on, the Car Access System 4 signals the status of Terminal 15 by switching on the power supply or broadcasting it via the K-CAN2. Direct power Supply from Terminal 15 has the advantage that the control units continue to be supplied from Terminal 15 even if terminal status messages are not received within a bus system, for example. In that way, emergency-mode functions can be maintained on the basis of terminal status if necessary.

The following control units receive the Terminal 15 status signal directly:
Those control units are:
• Driver’s-side footwell module, FRM
• Crash Safety Module, ACSM
• Instrument cluster, KOMBI
• Digital engine management module, DME
• Central Gateway Module, ZGM
• Electronic transmission control EGS
• Steering column switch cluster, SZL
• Integrated Chassis Management, ICM

Switching Off Terminal 15
Terminal 15 can be switched off by pressing the START-STOP button, a change of status to Terminal 0. Terminal 15 is automatically switched off if the following conditions occur:
• Vehicle double-locked by double-lock command.
• Battery reaching upper starting capacity limit.
• Car-wash special mode, switch-off takes place after 15 or 30 minutes.

Switch-off inhibitors
Automatic switching off of Terminal 15 may be prevented if the following conditions occur:
• Vehicle is moving, road-speed signal.
• Engine running.
• Brake pedal operated.
• Gear selector lever in position N, time-limited for special Car Wash mode.
• Low beam headlights ON Not when vehicle double-locked.
• Vehicle in transport mode status when coding in progress.
• Communication with the OBD.
• Switch-off inhibitor diagnosis.

Terminal 15N
Terminal 15N is switched on via a relay by the Car Access System. There is a relay fitted both
in the front and rear power distribution boxes for the purpose.

Relay for Terminal 15N
The control modules connected to Terminal 15N are connected to the vehicle power supply shortly after Terminal 15 is switched on.

Switching Off Terminal 15N
Before Terminal 15 is switched off, the control modules that are connected to Terminal 15N are notified that Terminal 15N is to be switched off. After Terminal 15 is switched off, the control units connected to Terminal 15N have five seconds time to save their data. After those five seconds have elapsed, the Car Access System 4 switches the relay off. At that point, the control modules concerned are switched off under defined conditions.

Terminal 15WUP (Wake-up)
Before the DME assumes sleep mode, it informs the IBS of the current SoC of the battery. The IBS sends the wake-up signal when the available SoC is used up. The DME obtains information on the current SoC of the battery from the IBS. The IBS informs the DME when the SoC of the battery is critical. The DME requests the stationary electrical loads/consumers to switch off. The DME no longer permits the IBS to wake the vehicle. The vehicle subsequently reassumes sleep mode. The wake-up function only applies when the vehicle is at rest.

Terminal R
The status Terminal R ON can only be selected if the engine has been stopped by briefly pressing the START-STOP button. The status Terminal R ON/Terminal R OFF is purely a bus signal. The Car Access System broadcasts the signal on the K-CAN2. Consequently, the F01/F02 does not have a separate lead for Terminal R! Terminal R is switched off under the following conditions:
• START-STOP button pressed
• Vehicle double-locked by double-lock command
• Time limit of 8 minutes not exceeded
• Battery upper starting capacity limit reached

Functional Reliability of Switchable Terminals
In order to increase the functional reliability of the vehicle's power supply, Terminal 30F, Terminal 30B and Terminal 15N can not be switched off under the following conditions:
• Terminal 15 ON
• Vehicle moving
• Engine running

The Car Access System has two processors that are responsible for terminal control. The software on the main processor and coprocessor prevents undefined switch-off of
Terminal 15 and switch-on of Terminal 50. Terminal 30F is safeguarded by the status of Terminal 30B. That means that when Terminal 30B is on, Terminal 30F can not be switched off.

ID Transmitter Search in Passenger Compartment (Keyfob)
When the START-STOP button is pressed, it triggers the search for an ID transmitter in the passenger compartment. The passenger compartment search is required for the
Passive Go function in order that starting can be enabled. When performing the passenger compartment search, the Car Access System 4 issues a request for an ID transmitter to register with the vehicle. There are two antennas provided for the passenger compartment search. One antenna covers the front of the passenger compartment and the other the rear. The antennas are connected to the Car Access System 4. The Car Access System 4 sends out a signal with a frequency of 125 KHz through the antennas. That signal triggers the ID transmitter to register with the vehicle. The ID transmitter responds with an encrypted radio signal. The remote control receiver in the diversity module passes the radio signal information to the Car Access System 4 via the LIN bus. The Car Access System checks whether the ID transmitter belongs to the vehicle. Subsequent communication takes place on the ID transmitter’s transmission frequency, e.g. 315 MHz. The Car Access System 4 checks whether the ID transmitter matches the vehicle. If the check is positive, the Car Access System 4 enables terminal control. The individual terminals can then be selected.

State of Charge

SoC is a calculated condition showing the current charge in the battery. The SoC calculations are performed by the DME. SoC is used during key off periods to insure the battery maintains a sufficient charge to start the engine at least one more time.

State of Health
SoH tracks the history of the battery in the vehicle. Charge/discharge cycles and times are monitored. SoH helps the DME determine the proper charging rates and anticipated battery life.

The IBS detects vehicle start based on current draw in excess of 200A. The engine running signal is made available by the DME via the BSD. Internal resistance of the battery is calculated from the current and voltage dip. These indicators are forwarded to the DME. From this data, the DME the state of health (SoH) of the battery.
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New Member
Mar 6, 2020
My bmw 118d had a power overload due to a spanner in the boot falling inside the battery housing, car starts runs and drives fine, but headlights and rear lights are permanently on, no front windows, no center console or interior lights working, snap on diagnostics sais (terminal 30 switched off) I’ve changed relay 30b but can’t seem to locate terminal 30 ? Any advice would be great or any idea of where to start