Functional description

The seat heating can be switched on separately for the driver's seat and front passenger seat as of terminal 15 ON using the buttons in the control panel of the IHKA (integrated automatic heating and air conditioning system).

• Vehicles with seat module:

  The IHKA control unit processes each button signal and sends a message across the K-CAN (body CAN) to the driver seat module (SMFA) and/or passenger seat module (SMBF).

• Vehicles with seat-heating electronics:

The button signals are transmitted via the body CAN to the junction box electronics (JBE), the Body Domain Controller (BDC) or the front electronic module (FEM) by the IHKA control unit.

• Vehicles with front electronic module(FEM):

The front electronic module (FEM) outputs the request as a message to the rear electronic module (REM) on the body CAN.

According to the selected heating stage, the rear electronic module (REM), the Body Domain Controller (BDC) or the junction box electronics (JBE) output a temperature signal as a message to the driver seat-heating electronics or the front passenger seat-heating electronics on the LIN bus.

The first time the button for the seat heating is pressed, the seat module or the seat-heating electronics activates the seat heating and thus the backrest heating. Heating stage 3 (high heat output) is switched on. Further keystrokes switch on the next-lowest heating stages 2 and 1 (medium and low heater output) or switch off the seat heating.

Depending on the selected heating stage, the seat module or the seat-heating electronics generates a pulse-width modulated signal (PWM signal) that is used to operate the seat heating pad in the backrest. The backrest heating is monitored by a temperature sensor (NTC resistor).

Courtesy of BMW OF NORTH AMERICA, INC.