Front Heated Seats Function - GF91.30-P-0004KJ
MODEL 453.0 (except 453.091), 453.3 (except 453.391), 453.4 (except 453.491)
with CODE 873 (Seat heating for driver and front passenger)
MODEL 453.091/391/491
with CODE 873 (Seat heating for driver and front passenger)
except CODE U14 (Climate package)
Shown on LHD Model
Function requirements, general
- No undervoltage or overvoltage (consumer shutoff not active)
- Circuit 15 ON
The respective seat heater control unit receives the status of circuit 15 ON and therefore also the power supply via a direct electrical line from the vehicle interior fuse and relay module. To do so, the ignition lock switches a relay in the vehicle interior fuse and relay module, which connects circuit 15g to the respective seat heater control unit.
Seat heater (SIH), general
With the seat heater, it is possible to heat the seat cushions and the backrests. The respective seat heater is activated using the front seat heater switch and actuated by the seat heater control unit integrated into the front seat cushion heater pad. Using the seat heater temperature sensor integrated into the seat heater control unit, the seat heater control unit determines the seat cushion temperature and actuates the respective seat cushion heater pad and backrest heater pad accordingly.
The driver seat heater control unit actuates the following heater pads (described on left-hand drive vehicle):
- Left front seat cushion heater pad
- Left front seat backrest heater pad
The front passenger seat heater control unit actuates the following heater pads (described on left-hand drive vehicle):
- Right front seat cushion heater pad
- Right front seat backrest heater pad
The respective seat heater control unit and the respective seat heater power supply solenoid switch are part of the respective front seat cushion heater pad or the respective wiring harness in the front seat cushion heater pad. The seat heater control unit and the seat heater power supply solenoid switch cannot be exchanged separately.
The respective seat heater control unit receives the supply voltage for the heater pads via the seat heater power supply solenoid switch integrated into the wiring harness. The seat heater power supply solenoid switch is actuated by the fuse and relay module when the ignition is switched on (circuit 15 ON). It then connects the power supply (circuit 30g) to the seat heater control unit. The supply voltage (circuit 15g) of the seat heater control unit itself is also switched by the vehicle interior fuse and relay module as soon as circuit 15 is switched on, which is why the seat heater can only be operated if the ignition is switched on and the seat heater is switched off automatically as soon as the ignition is switched off (circuit 15 OFF).
The SIH function includes the following subfunctions:
- Function sequence for manually switching on/off
- Function sequence for automatic switch off
Function sequence for manually switching on/off
Operation takes place via the respective front seat heater switch, which is installed on the side paneling of the respective seat. The front seat heater switch is read in via a direct electrical line by the seat heater control unit. If the seat heater control unit recognizes the signal of the front seat heater switch, it activates the seat heater by actuating the respective seat cushion heater pad and the backrest heater pad. The respective seat cushion heater pads and backrest heater pads are connected in series. If the seat heater was activated, the seat heater control unit actuates the status LED in the front seat heater switch via a direct electrical line. The heating element of the respective heater pad consists of a PTC thermistor cable (positive temperature coefficient (PTC)), which means that the power consumption decreases with increasing heater pad temperature. The seat heater control unit switches off the seat heater as soon as it recognizes a status change of the front seat heater switch, at which point it deactivates the status indication.
Function sequence for automatic switch off
The timer control is implemented by the respective seat heater control unit and is divided into the following subfunctions:
- Automatic timer shutoff function
- Automatic shutoff in case of overtemperature, function
Automatic timer shutoff function
If the seat heater is active for t = 12 min, the seat heater control unit switches off the seat heater independently. The LED status indication in the front seat heater switch goes out. However, the seat heater can be switched on again for t = 12 min.
Automatic shutoff in case of overtemperature, function
If the seat heater control unit recognizes overtemperature using the seat heater temperature sensor integrated into the seat heater control unit, it switches off the voltage supply to the seat cushion heater pad and backrest heater pad. If the heater pad temperature has dropped to a certain specified value, the voltage supply is switched on again. The LED status indication in the front seat heater switch remain on during this process.
| Electrical function schematic, seat heater (SIH) | PE91.30-P-2050-97BBA | ||
| Overview of system components of comfort heating systems | GF91.30-P-9990KJ |