Fuse Block: Description and Operation

Junction Box Electronics

junction box electronics
The junction box plays a central role in the vehicle. In the junction box, the distribution box and junction box electronics form a unit. The junction box electronics is no longer the central gateway in the vehicle.

Brief description of components
The junction box consists of the distribution box and the junction box electronics.

JBE: junction box electronics
The junction box electronics unit combines numerous functions in a single control unit. The junction box electronics unit is connected via 4 plug connections.
A 54-pin connector is for the connection to the dashboard. Two other connectors are for the connection to the main wiring harness. These are 54-pin and 47-pin connectors. A 23-pin internal plug-in connection connects the junction box electronics directly to the distribution box.

PDC: electronic parking aid
From the F01 onwards, the hardware of the electronic parking aid is integrated in the hardware of the JBE control unit. The function of the parking aid has a separate processor. This is why the parking aid has no address of its own on the CAN bus. The parking aid can be treated as a separate control unit with regard to diagnosis. The PDC control unit has its own fault code memory and is listed separately in the control unit functions.
As the hardware of the PDC control unit is integrated in the hardware of the JBE control unit, the JBE control unit supplies power to the PDC control unit.

Distribution box
The fuses and various plug-in and soldered relays are located in the distribution box of the junction box. Depending on the vehicle equipment, the boards of the distribution box are fitted with different relays. There is an opening in the lower part of the junction box.
The junction box electronics are connected to the distribution box through this opening.

System functions
Numerous functions are provided in the junction box electronics (JBE). The junction box electronics perform a great many controlling tasks.
Depending on the model series and equipment variant, the following functions can be controlled or signals detected by the junction box electronics:
- Power windows
- Wipe/wash system
- Central locking
- Climate control
- Seat heating
- Mirror heating and heated washer jets
- Bi-stable relay
- Functions for instrument cluster
- Roller sunblind for the rear window
- Roller sunblinds on the rear driver's side and rear passenger's side
- Roller cover for luggage compartment
- Interior rearview mirror
- Electronic parking aid

Power windows
The footwell module (FRM) and the junction box electronics (JBE) control and monitor the power windows.
The junction box electronics unit detects the following signals and makes them available to other bus subscribers:
- Power windows switch, front door on passenger's side
- Power windows switch, rear door on passenger's side
- Power windows switch, rear door on driver's side
- Hall sensor, rear door on driver's side
- Hall sensor, rear door on passenger's side

The junction box electronics control the following actuators:
- Power window drive, rear door on passenger's side
- Power window drive, rear door on driver's side

Wipe/wash system
The junction box electronics unit detects the following signals and makes them available to other bus subscribers:
- Front reset contact
- Rear reset contact

The junction box electronics control the following actuators:
- Wiper module connected via LIN bus
- Wiper relay for rear window
- Washer pump relay for headlight-cleaning system

Central locking
The junction box electronics (JBE) are the executing control unit for the central-locking system. The junction box electronics handles activation of all the central-locking drives. The following control combinations are possible:
- Selective unlock
- Deadlock release
- Locking
- Unlocking and deadlock release
- Deadlock

The luggage compartment lock is activated via its own final stage.

Climate control
The junction box electronics (JBE) unit detects the following signals and makes them available to other bus subscribers:
- Sensor for automatic air recirculation mode
- Refrigerant pressure sensor
- Rear stratification control

The junction box electronics control the following actuators:
- Additional coolant pump
- Control valve for air conditioning system or magnetic clutch
- Water valve (depending on engine)

Seat heating
For seat heating, a seat heating module or the higher-quality driver seat module can be installed. A seat module is always installed with seat memory. The junction box electronics (JBE) send a query to determine whether seat module is installed. If the junction box electronics do not receive confirmation, the junction box electronics handle activation of the seat heating. The junction box electronics generate a pulse-modulated signal. This signal activates the seat heating module.
If a seat module is fitted, the seat heating is activated directly by the seat module.

Mirror heating and heated washer jets
The junction box electronics (JBE) control the following actuators:
- Basic version of the mirror heating
- Jet nozzle heating

If mirror memory is installed, the footwell module (FRM) controls it via the LIN bus.

Bi-stable relay
The bi-stable relay is used to shut down terminal 30g-f if there is a closed-circuit current fault. The relay is only fitted for certain optional extras (e.g. CIC, TCU, ULF). If a bi-stable relay is fitted, an intelligent battery sensor is also fitted

Functions for instrument cluster
The junction box electronics unit detects the following signals for the instrument cluster:
- Fuel level sensor 1
- Fuel level sensor 2
- Coolant level
- Washer fluid level

Roller sunblind for rear window
The junction box electronics (JBE) actuate the drive for the roller sunblind.

Roller sunblinds on the rear driver's side and rear passenger's side
The roller sunblinds on the rear driver's side and rear passenger's side are each connected to the junction box electronics via a LIN bus.

Roller cover for luggage compartment
The junction box electronics actuate the drives for the roller cover in the luggage compartment.

Interior rearview mirror
The junction box electronics activate the functions of the interior rearview mirror.
The interior rearview mirror is connected to the junction box electronics via the LIN bus.

Line connection
As well as its electronic function, the junction box electronics unit (JBE) also have a connector function. Many of the cables in the 4 connectors connected to the junction box electronics are interconnected via the junction box electronics. The connections optimize the wiring harness. Here, the junction box electronics functions as a nodal point.

Relays of the junction box electronics
The junction box electronics (JBE) have internal and external relays. The excitation coils on all relays are permanently supplied with a positive cable. The positive power supply for the external relays is provided via the load circuit which is to be switched through. The positive power supply of the internal relay lies on the secured supply cable of the junction box electronics. All relays are controlled via the negative lead. All internal relays and the relay for wiper stage 1 and wiper stage 2 are located downstream of the fuse on the current circuit. All other external relays of the junction box electronics lie in the current circuit before the fuse. Internal relays are:
- Relay for power window drive, rear
- Relay for the central-locking drive (except for luggage compartment lid)

The external relays are:
- Relay for drive, rear window wiper
- Relay for headlight-cleaning system
- Relay for heated rear window
- Bi-stable relay (deactivation of closed-circuit current fault)

electronic parking aid
From the F01 onwards, the hardware of the electronic parking aid is integrated in the hardware of the JBE control unit. As the function of the electronic parking aid has its own processor, it has its own address on the CAN bus. This is why the electronic parking aid can be treated as a separate control unit. For details, see functional description for the PDC control unit.

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