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 Advaned Air Bags and Pressure on the Back of the Front Passenger Seat
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Question
    Why do some vehicle manuals warn that nothing should press against the back of the front passenger seat or be placed under that seat?

Short answer
    Pressure on the seatback may cause a false reading by the sensors that regulate the passenger-side advanced air bag (AAB), possibly causing either the AAB to deploy when it is not needed or to be suppressed when it is needed. The same problem could occur if objects under the front passenger seat (like stowed medical equipment) get caught between the seat rails or if a rear passenger lifts the seat cushion by pressing with his/her feet. 
    This advice impacts CPS since pressure may be applied to the front seatback when a rear-facing CR is squeezed into a small rear seat space or when a child in a forward-facing CR is able to push his or her feet against the seatback.

Background
   Deborah Stewart, editor of Safe Ride News, was asked by a CPST at the 2009 Lifesavers conference about a warning in the 2006 Honda Odyssey manual against putting pressure against the back of the front passenger seat. When she followed up with a contact at Honda, he stated that the reason for this warning is that such pressure could affect how the AAB responds.
      An AAB should be “off” when it is unoccupied or occupied by an undersized passenger, such as a child in a CR. Many AABs rely on sensors that measure pressure/weight on the passenger front seat and use of the lap-shoulder belt to determine whether the air bag is on or off. Pressure on the top or back of the passenger seat, such as from a rear-facing CR pressing on or wedged against the seatback, or a child pushing his/her feet against the seat, could affect AAB systems that have weight sensors in the seat track.
    SRN’s source at Honda explained that even CRs installed in the center rear that are wedged between the front seats can affect the sensors in the passenger seat.  Some seat weight sensors are mounted on only one side of the seat track for some manufacturers vehicles, so pressure on the opposite side would result in a false reading indicating more weight than is actually in the seat, while pressure on the near side would indicate less weight.
    (Note that there is no pressure sensor for the AAB in the driver’s seat, so this condition affects only the passenger seat.)

What CPSTs Need to Know
     When working with caregivers, CPSTs should find out whether the vehicle has AABs.  When AABs are present, owners should be informed that back seat occupants should not put pressure on the passenger front seatback or under that seat.           
     AABs began to be phased in with the 2003 model year and have been in all cars, minivans, light trucks, and SUVs since the 2006 model year. Check both the air bag and CR sections of the vehicle owner’s manual for details.
    If a RF CR presses against the front passenger seatback when installed, consider these options:
  • Install the CR in the driver-side position instead.
  • Put the CR handle (if present) in the upright or fully lowered position, if allowed by the CR manufacturer.
  • Use a CR that takes less fore-aft space in the rear-facing mode.
  The Honda representative clarified that touching or light contact by a CR is okay, describing “light contact” as that which would allow a sheet of paper to be easily pulled out from between the contact point of the CR and the seatback.  Though this guideline would likely apply to vehicles of other makers, caregivers should check with their specific automaker.
   When AABs are present, also avoid pressure to the front passenger seat that may be applied by:
  • a tightened (or over-tightened) RF tether.
  • the legs of forward-facing children who are stretching or pushing.
  • medical equipment, such as oxygen and monitors, that must somehow be stowed for travel .
(Note: CR instructions may also have advice about whether the CR may touch the vehicle seat that may or may not be dependent on the presence of an AAB.)

©Safe Ride News Jan/Feb 2010

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