Brief component description

The following components are described:

• Crash-active head restraint
• ACSM or MRS: Crash safety module or multiple restraint system (ACSM stands for "Advanced Crash Safety Module", referred to as the "crash safety module".)
• Airbag control lamp

Crash-active head restraint 

The crash-active head restraint is available for the driver's and front passenger seat. From the outside the Crash-Active Head Restraint is distinguished by its two sections, which give it an easily recognized appearance. The Crash Active Head Restraint is available in two versions:

• Crash-active head restraint for the comfort seat

  The depth adjustment of the head restraint can be set via the backrest upper section adjustment.

• Crash-active head restraint for all seats except comfort seat

  The button for setting the head restraint (depth adjustment) is installed in the side face of the front section of the head restraint. It enables the position of the front section of the head restraint to be varied in 3 positions by up to 30 millimeters depending on what the occupant wants. For the forward depth adjustment, the front section of the head restraint only needs to be pulled (2 lock positions). For the backward depth adjustment, press the button in the front section of the head restraint. This releases the latch mechanism. The front section of the head restraint can be pressed backwards.

Spring force instantaneously propels the head restraint's front section into place in response to rear impacts. It moves forward by up to 60 millimeters, and upward up to 40 millimeters (depending upon the momentary height adjustment). This reduces the distance to the head.

Fig 1: Removing Crash-Active Head Restraint

Courtesy of BMW OF NORTH AMERICA, INC.

When the Crash Active head restraint module or MRS control unit transmits a trigger signal, the Crash Active head restraint deploys as follows:

• The ignition squib in the pyrotechnic component ignites the propellant charge. The pyrotechnic component contains the ignition squib and propellant charge (designation in the wiring diagram: "Alternator active head restraint front left" and "Alternator active head restraint front right").
• The propellant charge drives a pin. The pin presses onto a release plate.
• When the release plate shifts, the preloaded springs are triggered. The spring force moves the front section of the head restraint forward and upward.
  Fig 2: Identifying Crash Active Head Restraint Module Components

  Courtesy of BMW OF NORTH AMERICA, INC.