Function Of Rear Heated Seats - GF91.30-P-0005GN

MODEL 166

as of model year 2016

with CODE 872 (Heated rear seats)

MODEL 292

with CODE 872 (Heated rear seats)

Function requirements, general

Circuit 15R ON

The electronic ignition lock control unit sends the circuit 15 status over the interior CAN to the rear control unit.

Seat heater (SIH) for rear seats, general

The seat heater enables the seat cushions and backrests of the rear seats to be heated in three heater stages.

The seat heater function encompasses 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 left rear seat heater button, 2nd seat row and the right rear seat heater button, 2nd seat row in the RCP [HBF] control unit.

The RCP [HBF] control unit reads in the status of the left rear seat heater button, 2nd seat row and the right rear seat heater button, 2nd seat row directly and transmits this via the interior CAN to the rear control unit.

The rear control unit then actuates the following heater pads directly depending on the request:

Left rear seat sitting surface heated cushion
Left rear backrest heated cushion
Right rear seat sitting surface heated cushion
Right rear backrest heater pad

The rear control unit continuously checks the function of all involved components of the seat heater and sends the corresponding status via interior CAN to the RCP [HBF] control unit. In accordance with the frequency with which the respective rear seat heater button is pressed, the RCP [HBF] control unit actuates the LEDs in the respective rear seat heater button directly.

Press once: 3 LEDs illuminate, stage 3 of seat heater activated (P = 100%).
Press twice: 2 LEDs illuminate, stage 2 of seat heater activated (P = 65%).
Press three times: 1 LED lights up, stage 1 of seat heater activated (P = 35%).
Press four times: All LEDs off, seat heater switched off.

If the front seat heater switch is pressed again with the same circuit status, heating level 3 is provided with only P = 90 % of the heat output. The heat output of the respective heating levels can be adjusted in the factory using a diagnostic tester.

Function sequence for automatic switch off

The seat heater is automatically switched to the next lower heating level or switched off completely depending on the time. The timer control is realized by the rear control unit.

Heating level 3 is active for t = 8 min.
Then the system automatically switches to heating stage 2.
Heating stage 2 is active for t = 10 min.
Then the system automatically switches to heating stage 1.
Heating level 1 is active for t = 20 min.

Then the seat heater is automatically switched off.

The time settings for the three heating levels can be adjusted in the rear control unit using the diagnostic tester.

Other shutoff criteria:

Shutoff in the event of a hardware defect:
If actuation of the heater pads is detected without a request from a rear seat heater button, the power supply to the seat heater is switched off.
Switching off if temperature of printed circuit boards in the rear control unit is too high:
- Heating stage 3 can no longer be activated if the PCB temperature is T > 70 °C.
Heating stage 3 and heating stage 2 can no longer be activated if the PCB temperature is T > 80 °C.
The seat heater can no longer be activated if the PCB temperature is T > 90 °C.
If no circuit board temperature value is present, the outside temperature value is used instead.

If the PCB temperature reaches T > 90 °C, a fault message is stored in the fault memory. Manual switch on requires a cooling down of T = 2 °C for the corresponding temperature threshold.
Shutoff in the event of an error (short circuit, overload or open circuit (line break)):
The rear control unit detects a possible short circuit, overload or a line break in the respective heater pad and deactivates the power supply. The fault sources that have been listed can be diagnosed individually for each heater pad using a diagnostic tester.
Shutoff during engine starting procedure:
When the engine is started (cold start), the seat heater is deactivated for t = 20 s. During a hot start, the seat heater is deactivated for t = 3 to 5 s. The timer control continues to run, and the LEDs remain switched on. No undervoltage is detected during startup.
Switching off by energy management:
In order to prevent the battery from discharging in all driving cycle phases, the state of charge is continuously evaluated. Depending on the situation, the HS [SIH] are also deactivated.

If the seat heater is switched off, the LEDs for the respective rear seat heater button initially remain switched on. If the on-board electrical system reaches its on-board electrical system voltage again within the next t = 3 min, the seat heater function is automatically activated. If the shutoff lasts longer than t = 3 min, the LEDs in the respective rear seat heater button are also switched off. If the shutoff continues and the function is requested again by pressing the respective rear seat heater button, the LEDs light up for t = 1.5 s and then go out.
Shutoff in the event of voltage loss:
If one of the two supply lines (circuit 30 or circuit 30g) of the rear control unit fails, the seat heater is switched off.
Shutoff after circuit 15R OFF:
With circuit 15R OFF and circuit 15C ON, timer control runs on for t = 5 min. If circuit 15R is switched on again, the seat heater is also switched on again.
Shutoff in the event of "Timeout error":
If the request of the RCP [HBF] control unit for actuating the seat heater is discontinued or a "Timeout period" from the electronic ignition lock control unit is recognized, the seat heater is switched off.

Shutoff at end of diagnosis:

After the diagnosis has finished, the seat heater switches off.

	Electrical function schematic, seat heater, rear seats		PE91.30-P-2055-97NBA
	Overview of system components of comfort heating systems		GF91.30-P-9990GN