Seat heater, function

P91.30-2478-76

N10/1 Front SAM control unit with fuse and relay module

N10/2 Rear SAM control unit with fuse and relay module

N72/1 Upper control panel control unit

N72/1s10 Left seat heater button

N72/1s11 Right seat heater button

N73 Electronic ignition switch control unit

R13/1 Left seat cushion heater pad

R13/2 Left backrest heated cushion

R13/3 Right seat sitting surface heated cushion

R13/4 Right backrest heated cushion

CAN B Interior CAN

CAN E Chassis CAN

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LIN 1 Instrument panel LIN

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Function requirements, general

 Circuit 15R ON

 The electronic ignition lock control unit sends the status of circuit 15 via the interior CAN to the rear SAM control unit.

Seat heater (SIH), general

Using the SIH, it is possible to heat the seat cushions and the backrests of the front seats in three heating stages.

The seat heater function comprises the following subfunctions:

 Function sequence for manually switching on/off

 Function sequence for automatic switch off

Function sequence for manually switching on/off

When the left seat heater button or right seat heater button is pressed in the upper control panel control unit, the seat heater function for the corresponding seat is requested.

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When seat heater button is pressed several times, one of the three heating levels can be selected, while the highest heating level is selected at the first press of the button. The heating level that is active in each case is indicated by red light-emitting diodes (LEDs) in the corresponding seat heater button (function feedback). When a seat heater button is pressed four times, the seat heater is switched off.

The upper control panel control unit reads in the status of the corresponding seat heater button directly and transmits it via instrument panel LIN, front SAM control unit and interior CAN to the rear SAM control unit.

The rear SAM control unit actuates the following heater pads to match the request:

- Left seat cushion heater pad

- Left backrest heated cushion

- Right seat sitting surface heated cushion

- Right backrest heated cushion

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The heat output of the seat heater depends on the heating level that has been selected using the seat heater button.

- Heat stage 3 P = 100%, indicated by three LEDs

- Heating stage 2 P = 70%, indicated by two LEDs

- Heating stage 1 P = 40%, indicated by one LED

 If the seat heater is selected again with the same circuit status, heating level 3 is provided with only P = 90% of the heat output.

Function sequence for automatic switch off

The timer control for the seat heater is integrated into the rear SAM control unit.

- Heating stage 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 stage 1 is active for t = 20 min.
Then the SIH is automatically switched off.

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 The time settings for the three heating stages can be adjusted in the rear SAM control unit via the IS tester.

When one of the following situations occurs, the seat heater is switched off automatically:

- Hardware defect:
If the heater pads are actuated without a currently present request via the seat heater button, the rear SAM control unit switches the seat heater off.

- Overtemperature of printed circuit boards in rear SAM control unit:

- Heating stage 3 can no longer be activated if the PCB temperature is T > 90°C.

- Heating stage 3 and heating stage 2 can no longer be activated if the PCB temperature is T > 100 °C.

- At a printed circuit board temperature T > 110 °C the seat heater can no longer be activated.

 If no plausible circuit board temperature value is present, the interior temperature value is used.

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- Engine start:
The timer control continues to run during engine start.
The function feedback continues to be active. No undervoltage is detected during startup.

- Circuit 15R Off:
The seat heater is switched off if circuit 15R is switched off. The timer control continues to run for t = 5 min as long as circuit 15C is switched on. If the circuit 15R is switched on again during this time, the seat heater is reset to the last active condition.

- Undervoltage or overvoltage:
In the event of undervoltage or overvoltage, the rear SAM control unit switches off the seat heater. The function feedback continues to be active. If the shutoff lasts longer than
t = 3 min, it is also switched off. If the on-board electrical system voltage returns to its normal level within t = 3 min, the seat heater starts again automatically.
If the seat heater is requested again by pressing the seat heater button, the LEDs in the seat heater button come on again for t = 1.5 s before going out again.