Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
System functions
The networking of its own control unit is required for the activation of the transfer box.
In particular: Transfer box, Dynamic Stability Control as well as Integrated Chassis Management via FlexRay. The VTG control unit is a bus user on the FlexRay network.
Example F0x, F1x
| Item | Explanation |
|---|---|
| 1 | Footwell module (FRM) |
| 2 | Dynamic stability control (DSC) |
| 3 | Transfer box (VTG) |
| 4 | Power distribution box, rear |
| 5 | Button Hill Descent Control (Hill Descent Control = HDC button) |
| 6 | Controller (CON) |
| 7 | Central information display (CID) |
| 8 | Car information computer (CIC) |
| 9 | Integrated chassis management (ICM) |
| 10 | Car access system (CAS) |
| 11 | Central gateway module (ZGM) |
Example F2x, F3x, F15
| Item | Explanation |
|---|---|
| 1 | Transfer box (VTG) |
| 2 | Dynamic stability control (DSC) |
| 3 | Front power distribution box, passenger's side |
| 4 | Body Domain Controller (BDC) or front electronic module (FEM) |
| 5 | Headunit (HU-H, HU-B) |
| 6 | Central information display |
| 7 | HDC button in center console operating facility |
| 8 | Integrated chassis management (ICM) |
The transfer box control unit activates the servomotor. Distribution of the drive torque is oriented upon the torque that can be supported by each axle.
The electronically controlled multidisc clutch smoothly distributes the drive torque as required to the front axle. The rear axle is always powered. This means that all of the drive torque is applied to the rear axle when the multidisc clutch is separated.
The drive torque is distributed as follows in normal driving with four-wheel drive:
- 40 % to the front axle
- 60 % to the rear axle
The transfer box control unit and servomotor cannot be replaced individually. They must be replaced together.
In consultation with the central driving dynamics control function in the Integrated Chassis Management (ICM) integrated in the master control unit, the Dynamic Stability Control (DSC) stipulates the setpoint value for all-wheel control of the xDrive function. The setpoint value depends on the tendency of the vehicle to oversteer or understeer and the wheel slip. The setpoint value is transmitted to the VTG control unit.
The VTG control unit regulates the locking torque at the multidisc clutch in the transfer box in response to the following factors:
- Demand for required locking torque (comes from the DSC control unit)
- Condition of the transmission oil (calculated in the VTG control unit).
- Multidisc clutch wear (calculated in the VTG control unit).
- Load on servomotor (calculated in the VTG control unit)
- Transmission oil temperature (calculated in the VTG control unit).
The VTG control unit supplies the following information to the DSC control unit:
- The locking torque currently set
- All calculated data
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.