Monday, September 1, 2014

We all expect our car’s airbag to work in the case of emergency.  So what happens when it has been automatically shut off without warning?

We thought something was wrong with the airbag shutoff switch in our 2012 Subaru Impreza.  We’d be driving along, and all of a sudden the passenger airbag would shut off, leaving the passenger unprotected.

So we called the dealer and had the switch checked (more than once!) No problem, we were told. Maybe the passenger shifted her weight and the switch turned off.

Then, this week, a service attendant mentioned that the on-off switch had nothing to do with weight. It was based on the amount of water in a person’s body.

The light went on in our minds. It turns out that the airbag would shut off after a few minutes when we were driving home from the beach and the passenger was wearing a wet swim suit or sitting on a wet towel! It would stay off until the seat dried out.

We checked this out. Here’s how one Subaru dealer explains this on their website:

Most Occupant Detection Systems measure the weight of the front seat passenger, to determine if the front passenger seat airbag should deploy.

All 2012 and 2013 Impreza and 2013 BRZ models use a new type of Occupant Detection System called Electrostatic Capacitance Sensor ODS. This system does not use weight to determine whether to turn the Occupant Detection System ON and OFF. 

The Electrostatic Capacitance represents a material's capability of storing an electrical charge. 

When water or anything with high moisture content is spilled on the front passenger seat cushion, the airbag is designed to remain OFF until the seat cushion is dry.  This will also be the case if the passenger has moisture on their clothing, such as rain-soaked pants or rain gear.  In each of these situations, the airbag status may remain OFF even if a passenger is seated.

Passengers are advised NOT to sit in the front passenger seat if the seat cushion is wet or if their clothing is wet. The best way to ensure proper operation is to keep everything off the front seat except a passenger. 

We don’t recall getting notice of this when we bought the car.  And it was clear that the service department staff didn’t always think of mentioning this system when an owner brought up the issue of the airbag cutoff. And if you search for “Subaru occupant detection system” or “Subaru passenger airbag shut-off” on the web, there is no official notice from the company.

There is no warning about this shut-off system on the passenger side visor. And, if you check the owner’s manual, there is nothing about this issue in the opening section’s safety precautions, although there is material about the speed and force of airbag deployment. Later, embedded on page 42, there is this advisory if you happen to turn to that page: “If the front passenger’s seat cushion is wet, this may adversely affect the ability to determine deployment.  If the seat cushion is wet, the front passenger should stop sitting on the front passenger’s seat. Wipe off water from the seat immediately, let the seat dry naturally and then check the SRS airbag system warning light.…”

Let’s say you’ve never noticed this “feature.” You’re driving home from the beach on a crowded highway at 60 mph with your family in a full car, and the passenger airbag shuts off. Perhaps you see the shut-off light suddenly illuminating. How exactly do you stop the front passenger from sitting in the front passenger’s seat? Perhaps you don’t even see the shut-off advisory light, in that you are focused on the holiday traffic. In either case, your passenger faces an unexpected hazard.

Many Subaru owners are outdoor types who will drive home after a jaunt to the beach or a hike in the wet woods. How many of them know they are in danger when they do so?

How and why did Subaru decide that this kind of automatic shut-off mechanism was superior to one based on body weight? Don’t they have an obligation to better inform the owners of these model cars? This is a product design lawsuit waiting to happen.


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