BMW 3 Owners & Service Manuals

BMW 3: Start-up system

Starter motor

The combustion engine B46 can be started via the conventional starter motor and the electrical machine.

The following table shows when and under which conditions the respective start option is used:

Start-up system

Auxiliary battery

Start-up system
G20 PHEV, auxiliary battery

  1. Safety battery terminal 2 (SBK2)
  2. Auxiliary battery
  3. Intelligent battery sensor 2 (IBS2)

The energy required by the starter motor is provided by the auxiliary battery. It is installed in the luggage compartment. The auxiliary battery is a lead-acid battery with a capacity of 60 Ah.

Similar to the 12 V battery, the current, voltage and terminal temperature of the auxiliary battery are measured by an intelligent battery sensor (IBS2). The results are then forwarded via local interconnect network bus to the superior control unit, the Electrical Machine Electronics (EME). The EME forwards the signal via CAN bus to the DME.

In the event of an accident of sufficient severity, the safety battery terminal (SBK2) ensures the disconnection of the positive battery cable between the auxiliary battery and starter motor. The safety battery terminal (SBK2) is located directly at the positive terminal of the auxiliary battery. The pyrotechnic activation of the safety battery terminal (SBK2) for the auxiliary battery is effected by the Advanced Crash Safety Module (ACSM).

The intelligent battery sensor (IBS2) receives the voltage supply via a line with a small cross-section from the safety battery terminal (SBK2) of the auxiliary battery.

A change of the auxiliary battery must always be registered.

The positive battery cable runs from the safety battery terminal (SBK2) to the starter motor.

Three other lines also leave from the safety battery terminal (SBK2):

  • One as a voltage supply for IBS2 (without fuse).
  • One to the BCU to charge the auxiliary battery (with 60 A fuse).
  • One to the EME (with 5 A fuse).

Battery charging unit

The charger unit for auxiliary battery consists of a control unit and a unidirectional DC/DC converter; it connects the start-up system with the standard vehicle electrical system. The charger unit for auxiliary battery is installed in the luggage compartment on the right-hand side.

More information is available in the chapter 9.3 "New control units in the G20 PHEV".

Jump start terminal point

Start-up system
G20 PHEV jump start terminal point

Next to the jump start terminal point is a label displaying the correct/incorrect polarity.


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