Functional description

• Seat occupancy detection for front passenger, European version (will gradually be replaced with a revised version beginning from 09/2010 for all series): 

  When a weight is placed on the seat, resistance in the seat occupancy mat changes. The seat is detected as not occupied up to a weight of approximately 12 kg (only applies if the seat-occupancy mat is installed between the cover and the foam insert of the seat).

  The seat occupancy detection function, however, also depends on the type of seat. e.g.: The material tension in a leather seat or a taut sports seat is already interpreted as pressure on the sensors. In such cases, a weight below 12 kg can trigger the "seat occupied" condition.

  The resistance value is transmitted to the Crash Safety Module (ACSM) via LIN bus. For example, if the passenger's seat is recognized as being occupied without the seat belt buckle switch sending a signal, a fasten belt warning will be emitted by the Crash Safety Module.

  Persons can only be detected correctly if they assume the correct seating position, as both halves of the seat have to be loaded simultaneously.

The following graphic shows the seat-occupancy mat using example F01 up to 07/2012.

Fig 1: Seat-Occupancy Mat With Pressure Sensors

Courtesy of BMW OF NORTH AMERICA, INC.

• Seat occupancy detection for front passenger, European version (revised version, will gradually be replaced beginning from 09/2010 for all series): 

  The seat-occupancy mat is installed on the underside of the foam insert.

The following graphic shows the seat-occupancy mat using example F01 from 07/2012.

Fig 2: Seat Occupancy Mat With Pressure Sensors

Courtesy of BMW OF NORTH AMERICA, INC.

• Front passenger seat occupancy detection, US version, via seat-occupancy mat with pressure sensors (up to 09/2009): 

  The seat-occupancy mat is installed on the underside of the foam insert. The crash safety module detects the seat occupancy status by evaluating the imprint on the seat cushion. This enables the crash safety module to decide whether to enable and disable the airbags on the passenger's side.

  The distances of the surfaces and centers of gravity on the occupied seat cushion indicate whether an adolescent or adult with required size, or a small child, is in the child restraint system specifically designed for the purpose. The airbags on the passenger's side are deactivated automatically when a small child is detected. The indicator light for front passenger airbag deactivation lights up. If a person of adequate size sitting correctly is detected, the airbags on the passenger's side are activated. The indicator light for the front passenger airbag deactivation does not light up.

  The front passenger airbag could deactivate with a youth or adult seated in certain positions (indicator light for passenger airbag deactivation comes on). In such cases, the seat position must be varied until the indicator light for front passenger airbag deactivation goes out (airbags activated).

The following graphic shows the seat-occupancy mat using example: F01.

Fig 3: Seat-Occupancy Mat With Evaluation Electronics

Courtesy of BMW OF NORTH AMERICA, INC.

• Front passenger seat occupancy detection, US version, via seat-occupancy mat with capacitive sensor system (from 09/2009): 

  The front passenger seat occupancy detection consists of a seat occupancy mat with a capacitive sensor system and evaluation electronics. The occupancy of the front passenger seat is detected by measuring the resistance of the human body.

  Classification of the occupancy status is based on the evaluation of the capacitive resistance. The electronic evaluation unit picks up the change and determines the corresponding status.

  The airbags on the passenger's side are deactivated automatically when a small child is detected in the child restraint system provided for this purpose. The indicator light for front passenger airbag deactivation lights up. If a person of adequate size sitting correctly is detected, the airbags on the passenger's side are activated. The indicator light for the front passenger airbag deactivation does not light up.

  The front passenger airbag could deactivate with a youth or adult seated in certain positions (indicator light for passenger airbag deactivation comes on). In such cases, the seat position must be varied until the indicator light for front passenger airbag deactivation goes out (airbags activated).

  NOTE: Electronic devices that are placed on the front passenger seat, e.g. laptop computers, mobile phones etc., could cause the front passenger airbag to activate.

  This behavior occurs primarily with devices that are connected to the vehicle electrical system via a USB cable or other charger adapter.

  In vehicles with an acoustic seat belt warning, this could cause the warning signal to sound.

  Moisture on the seat surface can also cause a faulty seat occupancy detection.

  The evaluation electronics in the electronic component transmits the status information in cycles to the Crash Safety Module. The data is transmitted via the LIN bus.

  If there is a breakage in the heating wire of the seat heating, the seat occupancy mat self-diagnosis makes a corresponding fault code entry in the Crash Safety Module.

The following graphic shows the seat-occupancy mat using example: F01.

Fig 4: Seat-Occupancy Mat With Evaluation Electronics

Courtesy of BMW OF NORTH AMERICA, INC.