Seat Heating, Right

Seat Heating

The seat heating system heats the seat cushion area and backrest. The electronics for controlling the selected heating temperature (3 stages) and fault monitoring are integrated in the switching center.

Function
Seat heating can be switched on in three heating stages as from terminal 15 by pressing the button. Three LEDs built into the switching center light to indicate operation. "Terminal 15 active" is signalled to the switching center via the K-bus.

Initially, heating stage 1 is activated when the seat heating is switched on (button pressed once). The seat surface is heated up to approx. 44 degree C. All three LEDs light to indicate operation.

By pressing the button once more, the topmost LED goes out and heating stage 2 is activated. The seat is now only heated up to 39 degree C.

The seat heating system is switched to heating stage 3 by pressing the button once again. The bottom-most LED lights. The seat is heated up to 35 degree C.

The seat heating is switched off by pressing the button once again or switching off the ignition. The seat heating can also be switched off in any heating stage by pressing the push button for longer than 1 second.

The seats are heated by means of carbon fibre heating mats in the main section and steel wires (steel filaments) in the bolster. A carbon fibre heating mat is installed in both the seat cushion section as well as in the backrest. The center sections of the seat and backrest as well as the bolsters of the seat and backrest are always heated. Heating filaments or carbon fibre mats are additionally integrated in the thigh support on sports seats. The seat and backrest bolsters are not heated on the series E39 sports seat with fabric cover.

The temperature is measured by a temperature sensor in the seat upholstery and passed on to switching center.

Monitoring functions

Battery voltage
The electronic seat heating control switches off the power supply to the heating mats if the battery voltage in the vehicle is less than 11.4 V ± 0.3 V. The function LEDs however remain on. Power supply to the heating mats is restored when the battery voltage is greater than 12.2 V ± 0.3 V for at least 5 seconds.

PC-Board temperature
Due to the fact that the power input of the seat heating system is very high (120 W), the temperature of the PC-board in the switching center is monitored by temperature sensors. Initially, the heating power is reduced as the temperature increases to over 85 degree C. The heating is switched off if the PC-board temperature exceeds 95 degree C. The function LEDs however remain on. The seat heating cuts in automatically again when the PC-board temperature drops below 85 degree C.

Fault monitoring
The electronic seat heating control system monitors the temperature sensor and heating mats for faults. Detected faults are stored in the fault code memory of the switching center.

The following faults can be recognized:
- Short-circuit or line break
- Short-circuit or line break of temperature sensors
- Break in heating mats

If a break or short occurs at the temperature sensor, the seat heating is switched off in order to prevent overheating. The function LEDs are switched off.