Hello,

I have a paraplegic adult daughter who is 4'8". I want to either permanently turn off or install a switch to conditionally turn off the passenger airbag as my daughter can't use the back seat.

Does anyone have advice on this?

Thanks!!

 

The car uses a mix of ultrasonics and weight sensing to determine if the airbag should be deployed or not, so it should be fine to leave it to make its own decisions. Why do you want to disable the airbag?

 

Thinking of disassembling the steering wheel. The airbag is disconnected after disconnecting battery for a few minutes. IOW there is a connector to do do.

I haven't removed the air bag behind the wood panel on passenger side, but it's got to have a connector too.

Probably going to cause a fault though won't it?

Any one know? Will a disconnected air bag harness produce an error message? What kind (IOW is it easy to ignore?)

It took many years and too many deaths to convince the US DOT to allow passenger air bag disable switches in cars. I doubt it was available or approved on any 2005 vehicles.

John

 

Unplugging it will cause a fault light and the owner's manual says that airbags may not operate in an accident. That makes it some big dice to roll in my book, if he just unplugs the pax airbag it would be making an assumption that the only fault is the unplugged bag so the rest should still go off.

Best choice would be to talk to specialist IMO.

 

there is a keyed system that is used in police cars for the front seat passenger position for over fifteen years. i believe it is to prevent the dash mounted computer and other police items from being propelled dangerously by an airbag deployment. this system disables the deployment without an error into the system. speak to a police conversion company or ask a local law enforcement office to put you in contact with the company that provided the vehicle conversions.


it is only a matter of finding out what circuits they switch. the kit that does this is a simple harness that is interfaced between the airbag system and the airbag harness. it is plug and play for frequently converted vehicles.


another avenue would be to contact a company that does conversions for disabled drivers and passenger as they install these switches.

 

I called the local dealer's service department. They can give me a circuit diagram to make the modification myself.

HOWEVER! I didn't realize that the car has sensors surrounding the passenger (they are hidden behind oval screens) that determine whether the airbag should deploy based on the weight and dimensions of who or what is in the front seat.

My next test is to confirm that when my daughter is in the seat, the disengaged airbag warning light is on. The light is on the dashboard in front of the passenger, it's very discreet.

 

Thanks to this thread, I now know why the airbag is off when my girlfriend is in the passenger seat. She is 5'3" and barely weighs 92 lbs. It seems the car thinks the seat is empty when she is sitting in it. Is there a way of making the system more sensitive so that it can detect petite females?

 

Feed her up. It'll be cheaper.

 

I'm going to guess that the seat knows it's not empty and the airbag disabled light comes on to note that deployment would cause more harm than good.

 

Wait, why would it cause more harm than good?

 

My guess would be physics and proximity to the airbag, i.e. the force of the airbag vs. the mass & dimensions of the occupant. You can play around with it if curious. The sensing circuit includes the seat belt latch so you can get:
- No seatbelt, no weight = no light
- Seatbelt latched, no/light weight = light on
- Seatbelt latched, weight on, lean towards the dash = light comes on.

 

The airbag is supposed to hit the occupant in the chest. If the person is too short (<=5'0") it will hit the face instead which could cause spinal cord injury or brain damage. More harm than good.

 

Martha,

Premise: "airbag will not deploy if seat is empty"

If this is true, then:

How I wonder does the car determine if the seat is empty.

1) weight sensor in seat - Sounds like someone confirmed there is a weight sensor in the passenger seat in one of the posts above.

If this is the only sensor used to determine seat occupancy, it seems to me it'd be really easy to put a switch in line with that sensor. Daughter in car, flip switch, opens circuit, car thinks seat is empty. Airbag will not deploy.

Drawbacks?
I can't think of anything beside the air bag that would be sacrificed by the car thinking the seat is empty. I know you can turn seat heater on with empty seat. Seat belt warning? (not a bit deal).

I can't think of anything significant that is influenced by presence / absence of passenger beside air bag deployment.

2) ultrasonic sensors - if these are used in combo with weight sensor or in place of weight sensor my idea is probably not going to work.

What do you (all) think?

John

 

As far as I know, no car is clever enough to use ultrasonics to detect the size of someone sitting in the passenger seat. I don't know the exact system used in these Jags, but generally there is a sensor in the seat to detect when someone is sitting in it. This will then bring on the seat belt warning until the passenger fastens their belt. This, in my experience, is normally pretty sensitive. I'm noticed that even leaving my brief case on the seat of some cars is enough for it to trigger the seatbelt warning.

Most passenger air bags that I have seen are a dual stage airbag. This consists of two firing devices on the one airbag module. There is often a sensor on one of the seat sliders that allows the seat to be adjusted backwards and forwards. This determines how far forward the seat is set. I would suggest that it uses a combination of this sensor and the seat pad to work out by how much to deploy the air bag. It may well also take into consideration the speed of the car and the airbag ECUs deccelerometer to also calculate whether to deploy both stages of the airbag.

Disconnecting the passenger airbag will trigger a fault in the airbag ECU which will most likely shut the whole system down. I have seen airbags disconnected and a 2 ohm resistor fitted to the plug from the ECU to trick it into thinking that the airbag is still connected. How this would affect the operation of the rest of the system in the event of an accident is dubious to say the least and I would not want to do it to any of my vehicles!

Personally, I wouldn't want to modify any airbag system in any vehicle. It's just not worth the risk in my opinion.

 

What is the status of a 20 year old airbag, and its components it needs to fire properly? What are the odds that the airbag is functioning as expected when being 20 years or even more? The oldest Xk8s are now 23 years old