A software glitch that could prevent certain airbags from deploying during collision.
Risk Level: Safety Critical
Japanese car-maker Nissan is recalling over 1 million vehicles affected by a software malfunction that may lead to airbag failure in a crash. The defect may have been caused by sensitive software just below the passenger seat.
The problem comes from the Occupant Classification System (OCS) algorithm, a system of sensors that detects who’s sitting in the passenger seat. The OCS eliminates the need for an on/off switch for airbags in most cases because it uses intelligent computer technology to identify whether an adult or a child is in the seat.
As we know that a problem stems from the OCS we need to take a closer look at the way it works.
So, inside the seat, we will find a pressure sensor, a silicone-filled “bladder”, and an electronic control unit (ECU). When someone sits on the seat, the pressure sensor signals the occupant’s weight to the ECU. The ECU then sends that data to the airbag, which has its own control unit. Based on that information, the vehicle’s computer turns the passenger airbag on or off.
The OCS doesn’t just detect weight. It reads the passenger’s seating position and determines if they’re wearing a seat belt. It also has a seat belt tension sensor that allows the OCS to interpret the pressure created when a child seat is fitted. In other words, the system is designed to tell whether a child safety seat is occupying that seat or whether you’re just carrying some heavy object there. A light on the instrument panel tells the driver whether the passenger airbag is on or off.
Once the onboard computer knows the passenger’s size and weight, the car’s airbags come into play. Based on the occupants’ size the airbags can deploy at full speed, partial speed, or not at all. An airbag deploying at full speed can badly injure or even kill a child or small adult.
According to a Nissan report, the OCS in affected vehicles “may not properly classify an adult passenger front seat occupant.” In particular, factors such as high engine vibration when a seat is empty and then filled, or “unusual occupant seating postures immediately upon sitting” can lead the OCS to believe that the front seat is empty. If the seat is believed empty, the passenger air bag status light does not turn on, meaning that an air bag could potentially fail to deploy in an accident.
This issue only affects the front passenger seat.
There have been no fatalities associated with this issue. However, there have been a handful of reports of the OCS system not performing as designed in a crash.
Nissan is working on a software upgrade now.
Nissan announced the recall of 1,053,479 vehicles to fix a software problem that could deactivate the front passenger airbag, including some of the auto-maker’s best sellers:
- 2013-2014 Nissan Altima (544,139 vehicles)
- 2013-2014 LEAF (29,165 vehicles)
- 2013-2014 Nissan Pathfinder MY (124,202 vehicles)
- 2013-2014 Nissan Sentra (182,569 vehicles)
- 2013 NV200/Taxi (6,696 vehicles)
- 2013 Infiniti JX35 / 2014 QX60 (63,698 vehicles)
- 2013 Infiniti Q50 (39,920 vehicles)
A potential failure can occur when an adult is classified as a child due to how he or she is sitting in the seat. Hence, the OCS will not send an activation signal to the airbag control and therefore the occupant of the seat is unprotected in a crash.
Taking into consideration all the known facts we think that some miscalculations in the seat occupant weight classification were made during the systems analysis and requirements definition phase of the system development.
There were no errors discovered during the code testing phase because the actual requirements were fulfilled correctly.
How to be avoided in the future
One of the possible solutions is to use a less sensitive sensors that read the seat occupant weight more accurately or refine the algorithm of the existing ones.
Another solution is to use a larger number of sensors in the seat detecting even a little change of a seat occupant position.