Electric seat ventilation, function

S91.30-4524-77

Function requirements, general

 'Circuit 15R ON' or 'Circuit 15 ON'

 The electronic ignition lock (EZS) control unit (N73) sends the circuit 15 or circuit 15R status via the interior CAN (CAN B) to the signal acquisition and actuation module (SAM) control unit (N10/1).

Seat ventilation, general

The seat cushions and backrests can be ventilated in 3 stages using the seat ventilation.

Function sequence for seat ventilation, general

The left 1st rear seat row seat ventilation button (S55/11s4) at the left 1st rear seat row electrical seat adjustment switch group (S55/11) or the right 1st rear seat row seat ventilation button (S55/12s4) at the right 1st rear seat row electrical seat adjustment switch group (S55/12) is used to switch the seat ventilation on and off and to regulate the ventilation output (initial condition of seat ventilation deactivated; all LEDs in the left 1st rear seat row seat ventilation button (S55/11s4) or right 1st rear seat row seat ventilation button (S55/12s4) off):

 First, the seat ventilation motors are actuated in the "suction" direction of rotation (seat cooling); after 10 minutes, the direction of rotation is reversed to "blowing" (seat ventilation).

 Press one time: 3 LEDs light up, stage 3 of seat cooling or seat ventilation activated (output power 100 %)

 Press 2 times: 2 LEDs light up, stage 2 of seat cooling or seat ventilation activated (output power 65 %)

 Press 3 times: 1 LED lights up, stage 1 of seat cooling or seat ventilation activated (output power 35 %)

 Press 4 times: All LEDs off, seat cooling and seat ventilation switched off

Function sequence for seat ventilation:

The left 1st rear seat row seat adjustment control unit with memory (N25/20) or right 1st rear seat row seat adjustment control unit with memory (N25/21) reads in the status of the left 1st rear seat row seat ventilation button (S55/11s4) or right 1st rear seat row seat ventilation button (S55/12s4) at the left 1st rear seat row electrical seat adjustment switch group (S55/11) or the right 1st rear seat row electrical seat adjustment switch group (S55/12).

The left 1st rear seat row seat cushion seat ventilation motors (M18/3) or right 1st rear seat row seat cushion seat ventilation motors (M18/5) and left 1st rear seat row backrest seat ventilation motors (M18/5) or right 1st rear seat row backrest seat ventilation motors (M18/6) are then actuated directly by the left 1st rear seat row seat adjustment control unit with memory (N25/20) or right 1st rear seat row seat adjustment control unit with memory (N25/21).

The left 1st rear seat row seat adjustment control unit with memory (N25/20) or right 1st rear seat row seat adjustment control unit with memory (N25/21) checks all involved components and sends the status via interior CAN (CAN B) to the signal acquisition and actuation module (SAM) control unit (N10/1).

The signal acquisition and actuation module (SAM) control unit (N10/1) also sends the status of the seat ventilation via interior CAN (CAN B) to the left 1st rear seat row seat adjustment control unit with memory (N25/20) or right 1st rear seat row seat adjustment control unit with memory (N25/21). The left 1st rear seat row seat adjustment control unit with memory (N25/20) or right 1st rear seat row seat adjustment control unit with memory (N25/21) then actuates the LEDs in the left 1st rear seat row seat ventilation button (S55/11s4) or right 1st rear seat row seat ventilation button (S55/12s4) accordingly.

Reduction of noise level:

In order to reduce the noise level of the seat ventilation when the vehicle is stationary, it is switched down to level 1 if the vehicle speed drops below 6 km/h. As of a vehicle speed of 9 km/h, the level that was originally selected is activated. The Electronic Stability Program (ESP) control unit (N30/4) sends the vehicle speed via the chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and interior CAN (CAN B) to the signal acquisition and actuation module (SAM) control unit (N10/1). The noise level reduction does not become active until 7 min after the respective seat ventilation has been switched on for the first time with the engine running.

Shut off criteria

A distinction is made between the following shutoff criteria:

 Shut-off in the event of a hardware defect

If actuation of the seat ventilation motors is detected without any pending request by the signal acquisition and actuation module (SAM) control unit (N10/1), the power supply to the seat ventilation is switched off.

 Shutoff in the event of an error (short circuit, overload or open circuit (line break))

If the left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21) detects a possible short circuit, overload or line break of the respective seat ventilation motor, it deactivates the power supply. The fault sources that have been listed can be diagnosed individually for each seat ventilation motor using a diagnostic system.

 Shutoff during engine starting procedure

When the engine is started (cold start), the seat ventilation is deactivated for 20 s. During a hot start, the seat ventilation is deactivated for 3 to 5 s. The timer control continues to run and the LEDs in the left 1st rear seat row seat ventilation button (S55/11s4) or the right 1st rear seat row seat ventilation button (S55/12s4) remain switched on as well.

 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 ventilation is also deactivated.

If the seat ventilation is switched off, the LEDs in the left 1st rear seat row seat ventilation button (S55/11s4) or the right 1st rear seat row seat ventilation button (S55/12s4) initially remain switched on. If the on-board electrical system reaches its on-board electrical system voltage again within the next 3 min, the seat ventilation function is automatically activated. If the shutoff takes more than 3 minutes, the LEDs in the left 1st rear seat row seat ventilation button (S55/11s4) or the right 1st rear seat row seat ventilation button (S55/12s4) are also switched off.

If the shutoff continues and the function is requested again via the left 1st rear seat row seat ventilation button (S55/11s4) or the right 1st rear seat row seat ventilation button (S55/12s4), the LEDs in the left 1st rear seat row seat ventilation button (S55/11s4) or the right 1st rear seat row seat ventilation button (S55/12s4) light up for 1.5 seconds and then go out.

 Shutoff in the event of voltage loss

If one of the two supply lines (circuit 30 or circuit 30g) to the left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21) fails, the seat ventilation is shut off.

 Shutting off after "circuit 15R OFF"

At "Circuit 15R OFF" and "Circuit 15C ON", the timer control runs on for another 5 min. If "circuit 15R" is switched on again, the seat ventilation is also switched on again.

 Shut-off in the event of "Timeout error"

If the request from the signal acquisition and actuation module (SAM) control unit (N10/1) to actuate the seat ventilation is missing or a "Timeout period" is recognized by the electronic ignition lock (EZS) control unit (N73), the seat ventilation is switched off.

 Shutoff at end of diagnosis

The seat ventilation is switched off after diagnosis is finished.