Seat Heating, Rear (With SMAFH/SMBFH Seat Module)

Seat heating, rear seats
The seat heating regulates the heat output according to what the user has specified

Brief description of components
Seat module, driver's side rear / passenger's side rear
The seat module is fitted in the luggage compartment.

The seat modules are networked with the vehicle via the CAN BUS.

Rear center console switch center
The control module rear center console switch center has the following functions:

CAN BUS interface to the vehicle electrical system

Interface to the seat switches

The control module rear center console switch center is fitted in the rear center armrest.

Operating switch rear driver's side / passenger's side rear
Depending on the equipment, various switch blocks are fitted.

The switch blocks are connected by means of ribbon cables to the rear center console switch center (BZMF).

Seat heating elements
The seat heating elements are resistor pads. There are 4 heating elements per seat:

a rapid heating field in the inner seat area

a rapid heating field in the backrest area

a residual heating field in the outer seat area

a residual heating field in the outer backrest area

Temperature sensors
Each seat is fitted with a temperature sensor at the heating element for recording the temperature. The temperature sensor is located between the heating elements.

The temperature sensor provides an average temperature that does not match the temperature of the seat surface.

This temperature value is only required for control of the seat heating.

Main functions
Seat heating
The desired heater setting can be set via the operating switch. The three LEDs indicate the corresponding heating stage.

The heating instruction is transferred from the switch block to the BZMF across a ribbon cable.

The BZMF sends the message across the K-CAN SYSTEM to the Car Access System (CAS).

The CAS as �gateway control module� passes the message on to the corresponding seat module via the K-CAN PERIPHERALS.

The seat module activates the heating elements directly.

Activation of the heating elements
When the seat heating is switched on, the rapid heating fields are activated first.

After the initial rapid heating, the residual heating fields are switched on.

All heating elements are activated in cycles. The duty factor depends on:

the selected heating stage

the ON period

and the heater field temperatures.

Operation of the seat heating
The seat heating is active as of terminal 15. Stage 3 is switched on with the first press of the button. Pressing the button again selects the next lowest stage or �off�. If the button is pressed for longer than 1.2 seconds, the seat heating switches off.

If the ignition is switched off briefly, the function mode of the heating is retained. The heating switched on again in the corresponding heating stage when the ignition is switched on again.

Safety function
Consumer shutdown

In the case of signal �Control peak reduction priority� from the power module, the power of the seat heating is reduced or it is switched off.

The function indicators (LEDs) remain switched on when the seat heating is switched off for a brief period.