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 seat.

The seat modules are linked across the K CAN SYSTEM data bus to the control units of the body area.

Rear centre console switch centre (BZMF)

The rear centre console switch centre control unit is

• the interface from the K CAN SYSTEM data bus to the control units of the body area and
  
• Interface to the seat switches
  

The control unit rear centre console switch centre is fitted in the rear centre 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 centre console switch centre (BZMF).

Seat heating elements

The seat heating elements are resistor pads. There are 4 heating elements fitted 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 the temperature recording system. The temperature sensor is located between the heating elements.

The temperature sensor provides an average temperature. This temperature does not correspond to the temperature on 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 selected displayed is indicated by one of the three light emitting diodes.

• The heating instruction is transferred from the switch block across a ribbon cable to the rear centre console switch centre (BZMF).
  
• The rear centre console switch centre (BZMF) makes the message available to the Car Access System (CAS) across the K CAN SYSTEM data bus.
  
• The Car Access System (CAS) is the ”gateway control unit” and it forwards the message across the K CAN PERIPHERALS data bus to the corresponding seat module.
  
• 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. The rapid heating sections heat with reduced power.

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

All heating elements are activated in cycles. The clocking 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 is switched on again in the last set heating stage when the ignition is switched on again.

Safety function

Load deactivation

In the case of signal ”Control peak reduction priority” from the power module, (PM), the power of the seat heating is either reduced or it is switched off.

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