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

Model 463 (except 463.342)

as of model year 2019

Show on model 463

Courtesy of MERCEDES-BENZ USA

Function requirements, general

Circuit 15R ON or circuit 15 ON:

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

Rear seat heater, general

The seat heater enables the seat cushions and backrests to be heated in three heating levels. The master control unit for the rear seat heater function is the rear SAM control unit.

The rear seat heater function comprises the following subfunctions:

Function sequence for switching seat heater on and off
Function sequence for left rear seat heater
Function sequence for right rear seat heater
Function sequence, automatic shutoff

Function sequence for switching seat heater on and off

The seat heating is switched on and off using the left rear passenger compartment seat heating button or the right rear passenger compartment seat heating button which also regulate the heating output (initial seat heating status is deactivated, all LEDs OFF):

Press one time: 3 LEDs light up, stage 3 of seat heater activated (100 % heat output)
Press two times: 2 LEDs light up, stage 2 of seat heater activated (65 % heat output)
Press three times: 1 LEDs light up, stage 1 of seat heater activated (35 % heat output)
Press four times: All LEDs off, seat heater switched off

If the seat heater is selected again with the same circuit status, heating level 3 is provided with only 90 % of the heat output. The heat output of the respective heating levels can be adjusted ex works using a diagnostic tester.

Function note

The seat heater is switched off automatically at a set time. The timer control is realized by the rear SAM control unit.

Heating level 3 is activated for 8 min. Then the system automatically switches to heating stage 2.
Heating stage 2 is activated for 10 min. Then the system automatically switches to heating level 1.
Heating level 1 is active for 20 minutes. The seat heater is then automatically switched off.

The timer control of the three heating levels can be adjusted ex works using a diagnostic tester.

Function sequence for left rear seat heater

The left rear door control unit reads in the status of the left rear seat heaters over the left rear door LIN and sends a corresponding request over the interior CAN to the rear SAM control unit. The rear SAM control unit evaluates this and sends a request to switch on the seat heater over the heater LIN to the rear seat heater control unit.

The rear seat heater control unit then actuates the following heater pads directly:

Left rear seat sitting surface heated cushion
Left rear backrest heated cushion

The rear seat heater control unit continuously checks the function of all the components involved in the seat heater and sends the corresponding status over the heater LIN to the rear SAM control unit.

Function feedback

To match the actuation frequency of the left rear seat heating switch, the rear SAM control unit sends the status of the seat heating over the interior CAN, left rear door control unit and the left rear door LIN to the left rear seat heating button, which actuates the LEDs in the left rear seat heating button accordingly.

Function sequence for right rear seat heater

The right rear door control unit reads in the status of the right rear seat heater over the right rear door LIN and sends a corresponding request over the interior CAN to the rear SAM control unit. The rear SAM control unit evaluates this and sends a request to switch on the seat heater over the heater LIN to the rear seat heater control unit.

The rear seat heater control unit then actuates the following heater pads directly:

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

Function feedback

To match the actuation frequency of the right rear seat heating switch, the rear SAM control unit sends the status of the seat heating over the interior CAN, right rear door control unit and the right rear door LIN to the right rear seat heating button, which actuates the LEDs in the right rear seat heating button accordingly.

Function sequence, automatic shutoff

The seat heater is automatically switched off when one of the following events occurs:

Shut-off in the event of a hardware defect
If the respective control unit reports an active actuation of the heater pads to the rear SAM control unit although a request has not been issued by a rear seat heater switch, the power supply for the heater pads is switched off by an integrated protection relay by the rear SAM control unit.
Deactivation in event of excess temperature of PCBs in respective control unit
- Heating stage 3 can no longer be activated if the PCB temperature is greater than 70 °C.
- Heating stage 3 and heating stage 2 can no longer be activated if the PCB temperature is greater than 80 °C.
- At a printed circuit board temperature of more than 90 °C, the seat heater can no longer be activated.

If the PCB temperature reaches more than 90 °C, a fault message is stored in the fault memory. Manual reactivation requires the printed circuit board temperature to drop to T = 2 °C below the corresponding temperature threshold.

If no circuit board temperature value is present, the interior temperature value is assessed instead. The climate control control unit sends the interior temperature value via the interior CAN to the rear SAM control unit.

Shutoff in the event of an error (short circuit, overload or open circuit (line break))
The respective control unit detects a possible short circuit, overload or a line break in the respective heater pad and then switches off the power supply. The fault sources that have been listed can be diagnosed individually for each heater pad using a diagnostic tester.
Shutoff when the engine starts
When the engine is started (cold start) the seat heater is switched off for 20 seconds. For a hot start, the seat heater is switched off for 3 to 5 seconds. The timer control continues to run, and the LEDs in the respective rear seat heater switch remain switched on. No undervoltage assessment takes place during startup.
Switching off by means of 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 seat heater is also switched off, if necessary. If the seat heater is switched off, the LEDs in the respective rear seat heater switch initially remain switched on. If the on-board electrical system returns to the specified voltage again within a period of 3 minutes, the seat heater function is also automatically restarted. If the shutoff takes longer than 3 minutes, the LEDs are also switched off. If the shutoff continues and the function is requested again, the LEDs illuminate for 1.5 seconds and then they go off.
Shutoff in the event of voltage loss
If one of the two supply lines (circuit 30 or circuit 30g) of the respective control unit fails, the seat heater is switched off.
Shutoff after circuit 15R OFF
For circuit 15R OFF and circuit 15C ON, the timer control runs on for another 5 minutes. If circuit 15R is switched on again, the seat heater is also switched on again.
Shut-off in the event of "Timeout error"
If the request of the rear SAM 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

The seat heater is switched off after diagnosis is finished.

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