Electric seat ventilation, function

P91.30-A000-79

P91.30-A001-79

 Model 205
as of model year 2016
with code 401 (Climatised front seats)
except code 221 (Electrically adjustable left driver seat)
except code 222 (Electrically adjustable right driver seat)
except code 242 (Front passenger seat, electrically adjustable with memory function)
except code 275 (Memory Package (driver's seat, steering column and mirror))
Model 253
with code 401 (Climatised front seats)
except code 221 (Electrically adjustable left driver seat)
except code 222 (Electrically adjustable right driver seat)
except code 242 (Front passenger seat, electrically adjustable with memory function)
except code 275 (Memory Package (driver's seat, steering column and mirror))
The front seat heater control unit in the front passenger seat functionally replaces the driver seat heater control unit and the front passenger seat heater control unit. In the following sections, only the term "seat heater control unit" is used.

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.

Seat ventilation, general

The seat cushions and backrests can be ventilated in three stages using the seat ventilation. The rear SAM control unit is the master control unit for the seat ventilation.

For vehicles with code 889 (KEYLESS-GO), the seat ventilation motors are initially actuated in the direction of rotation "seat cooling" in the case of convenience opening. If circuit 15R is then not switched on within 5 minutes or the vehicle is locked again, the seat ventilation is switched off.

On model 205 with code 577 (Remote activation of heating and ventilation systems) and on plug-in hybrid vehicles, the seat ventilation of the driver's seat can be switched on via the auxiliary climate control for a maximum of 60 s (after vehicle unlocking). The driver's seat is thus cooled down before departure.

Seat ventilation activation/deactivation

The seat ventilation is controlled via the seat ventilation switch in the respective seat climate control switch group. The left front door control unit reads in the status of the left front seat ventilation switch via the left front door LIN and sends it to the rear SAM control unit via interior CAN. The right front door control unit reads in the status of the right front seat ventilation switch via the right front door LIN and sends this to the rear SAM control unit via interior CAN.

For model 253 as of model year 2020, the seat ventilation can also be activated/deactivated via the voice control system (VCS). The head unit transmits in this case the relevant request via the user interface CAN, electronic ignition lock control unit and interior CAN to the rear SAM control unit.

The output of the seat ventilation motors can be set in three stages. When the seat ventilation is activated, the seat ventilation motors are operated at the highest stage.

 Stage 3: 3 LEDs are illuminated in seat ventilation switch. The seat ventilation motors are actuated at 100 % output.

 The seat ventilation motors are initially actuated in the direction of rotation "seat cooling". After 10 min, the direction of rotation is reversed (seat ventilation).

 Stage 2: 2 LEDs are illuminated in the seat ventilation switch. The seat ventilation motors are actuated at 65 % output.

 Stage 1: 1 LED lights up in the seat ventilation switch. The seat ventilation motors are actuated at 35 % output.

Driver's seat ventilation:

The rear SAM control unit evaluates the incoming request and transmits this in an equipment-dependent manner via one of the following connections:

 Via interior CAN to the driver seat control unit (with CODE 275 (Memory package))

 Over the heater LIN to the driver seat control unit (with CODE 221 (Left electrically adjustable driver seat))

 Via the heater LIN to the seat heater control unit (except code 275 (Memory package) and except code 221 (Left electrically adjustable driver seat))

The driver seat control unit or the seat heater control unit then directly actuates the following motor groups:

 Left front seat cushion seat ventilation motors

 Left front backrest seat ventilation motors

The driver seat control unit or the seat heater control unit continuously checks the function of all components involved in the seat ventilation and sends the corresponding status, depending on the vehicle's equipment, via one of the following connections:

 Via heater LIN to the rear SAM control unit (except CODE 275 (Memory package))

 Via interior CAN to the rear SAM control unit (with CODE 275 (Memory package))

The rear SAM control unit transmits the seat ventilation status via the interior CAN, left front door control unit and left front door LIN to the driver seat climate control switch group that accordingly actuates the LEDs in the left front seat ventilation switch.

Front passenger seat ventilation:

The rear SAM control unit evaluates the incoming request and transmits this in an equipment-dependent manner via one of the following connections:

 Over the interior CAN to the front passenger seat control unit (with CODE 242 (Electrically adjustable front passenger seat with memory function))

 Over the heater LIN to the front passenger seat control unit (with CODE 222 (Electrically adjustable right front seat))

 Via the heater LIN to the seat heater control unit (except code 242 (Electrically adjustable front passenger seat with memory function) and except code 222 (Right electrically adjustable front seat))

The front passenger seat control unit or the seat heater control unit then directly actuates the following motor groups:

 Right front seat cushion seat ventilation motors

 Right front backrest seat ventilation motors

The front passenger seat control unit or the seat heater control unit continuously checks the function of all components involved in the seat ventilation and sends the corresponding status, depending on the vehicle's equipment, via one of the following connections:

 Over the heater LIN to the rear SAM control unit (except CODE 242 (Electrically adjustable front passenger seat with memory function))

 Over the interior CAN to the rear SAM control unit (with CODE 242 (Electrically adjustable front passenger seat with memory function))

The rear SAM control unit transmits the seat ventilation status via the interior CAN, right front door control unit and right front door LIN to the front passenger seat climate control switch group that accordingly actuates the LEDs in the right front seat ventilation switch.

Reduction of noise level:

In order to reduce the noise level of the seat ventilation when the vehicle is stationary, the seat ventilation is switched back to stage 1 while the vehicle is stationary. The originally set stage is activated again from a vehicle speed of 9 km/h. The instrument cluster sends the vehicle speed via user interface CAN, electronic ignition lock control unit and interior CAN to the rear SAM control unit. The noise level reduction only becomes active 7 min after the seat ventilation is switched on with the engine running.

Automatic seat ventilation deactivation

The seat ventilation is automatically switched off (timed). The timer control is stored in the rear SAM control unit.

 Seat ventilation stage 3 is active for 8 minutes. Then it switches automatically to stage 2.

 Seat ventilation stage 2 is active for 10 minutes. It then switches automatically to stage 1.

 Seat ventilation stage 1 is active for 20 minutes. Then seat ventilation is automatically switched off. .

 The timer control can be changed using the diagnostic tester.

Other shutoff criteria:

 Shut-off in the event of a hardware defect

If the seat ventilation motors are actively actuated without a corresponding request, the rear SAM control unit accordingly requests deactivation of the power supply for the seat ventilation motors. The power supply for the seat ventilation motors is then deactivated by the seat heating control unit, the driver's seat control unit or the front passenger seat control unit.

 Shutoff in the event of a fault (short circuit, overload or line break)

The seat heating control unit, driver's seat control unit or front passenger seat control unit detects a possible short circuit, overload or a line break of the respective seat ventilation motor and deactivates the power supply. The listed fault sources can be individually diagnosed for each seat ventilation motor using the diagnostic tester.

 Shutoff when the engine starts

In the case of an engine start (cold start), the seat ventilation is deactivated for 20 s. During a warm start, the seat ventilation is switched off for 3   to 5s. The timer control continues to run, and the LEDs remain switched on. The voltage drop during the engine starting procedure is not evaluated as undervoltage.

 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 switched off if necessary.

When the seat heating is deactivated, the LEDs in the respective seat ventilation button initially remain switched on. If the on-board electrical system voltage is stabilized to normal voltage within the next 3 min, the seat ventilation restarts automatically. However, if the deactivation lasts longer than 3 min, the LEDs are also deactivated. If the deactivation persists and the function is requested again, the LEDs are illuminated for 1.5 s and then go out.

 Switch off in event of voltage drop

In the case of the failure of one of the two power supply lines of the seat heating control unit, driver's seat control unit or the front passenger seat control unit, the seat ventilation is deactivated.

 Shutoff after circuit 15R OFF

With circuit 15R OFF and circuit 15C ON, the seat ventilation is switched off. Timer control continues to run for 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 of the rear SAM control unit for actuating the seat ventilation is discontinued or a "Timeout period" from the electronic ignition lock control unit is recognized, the seat ventilation is switched off.

 Shutoff at end of diagnosis

The seat ventilation is switched off after diagnosis has been completed.