Air Bags Then and Now
I was looking some information up for this article when I came across a repair manual from the 60’s. There in the back of the book, with only one page of information, was “Air Cushion Restraint System” information. It had a drawing down in the lower right corner of a person sitting in the driver seat with an airbag deployed… the picture depicted an air bag that would completely cover the driver. It went from his forehead to his knees. His hand and arm position were completely in unnatural positions, and the airbag looked more like a parachute rather than what we see as airbags today. I had to chuckle at the information and the drawings. Very simple wiring, nothing complicated. The wiring system they showed consisted of a single harness, one sensor, a recorder (as it was called) and two air bags. In today’s terms I would call it a very simple circuit with a very uncomplicated component inventory, and probably just as unpredictable.
In the early 80’s a lot of attempts were made to move the production of the air bag systems into the standard production car. Back then a lot of cars had the horn button moved to the turn signal stock (you pushed in on the turn signal handle on a lot of them) and a large “boxy” fake horn pad was put in the center of the steering wheel. There were few manufacturers that offered the air bag as a standard feature but, the cars were being manufactured in a way that if they became available they could easily be added into the production line. By 1998 all new cars were required to have air bags as standard equipment. It took a new innovative part that allowed the horn and the air bag to be in the same place on the steering wheel. It’s now commonly called the “clock spring”. It’s nothing more than a thin wire tape rolled on its edge that takes on the appearance of a clock main spring. As the steering wheel is turned the tape either tightens up or loosens its windings. A good point to be made when taking the steering columns out these days, don’t turn the wheel to far or it can snap that thin tape of wire. I’d advise finding some way to secure the steering wheel and the steering shaft from rotating while it’s disassembled.
A study was done in December of 2001; a record was set with 7585 confirmed prevented deaths by proper airbag/seatbelt usage. If that isn’t enough to make you appreciate the air bag systems in today’s cars, I don’t know what will.
Generally, an airbag consists of sodium azide (NaN3) and potassium nitrate (KNO3) which when mixed together in the right proportions will produce nitrogen gas (N2) (rocket fuel). The estimated speed is around 150 to 250 mph as it leaves the steering wheel, which takes about 1/20th of a second. The powder substance that is accompanied with the blast is actually cornstarch or talcum powder. Neither of which is there for the explosion but is for coating the bag itself so that the material will stay pliable and lubricated to the point that it will not tear or deteriorate over a predictable time table.
According to the NHTSA (National Highway Traffic Safety Administration) it has been determined that the first 2 to 3 inches of the airbag explosion is the danger zone area. The recommended distance from the airbag is 10 inches from your breast bone. And, the proper position for the steering wheel is not centered on your face but centered on the breast plate. (Good thing to keep in mind with small children in the front passenger area or smaller drivers).
These days the systems have developed into fully enveloping curtains and complete passenger compartment protection. It’s a long way from the original systems offered at unbelievable prices in the late 50’s early 60’s. I found several old repair manuals dating back to those days that briefly (and I mean briefly) mentioned air bag systems. A lot of times it was in the same section of the manual with seat belts. (Passenger safety wasn’t high on the list of priorities back then) The original airbag systems were sometimes more expensive than the car itself. Surprisingly, did sell but whether or not they worked like the claimed they would I can’t answer that. I couldn’t find any statistics on early air bag usage. My guess is that they were not that reliable. But, with modern technology and the advanced electronics we have an affordable system that really… really works.
Diagnosing airbag systems is a matter of having the correct scanning equipment and the correct repair procedures. There are several manufacturers that offer a way to count the flashes of the airbag light for diagnostic purposes. (Wish more did the same). I have seen some of the manufacturers that offer the “read the flashes” method they also have less actual codes. When you look up the code it may refer you to a 4 digit code and a diagnostic tree at that point. I’ve also seen these 2 digit flash codes only be a generic code referring to a certain section of the air bag system. The diagnostics 2 digit code may not be able to tell the difference between the driver’s side and the passenger side.
After looking up the 2 digit code the diagnostics might even ask you to scan the vehicle with a scanner to determine which side it actually is. Sometimes, you can get by with the 2 digit codes, a lot of that may depend on the year of the vehicle. The older the car the more likely counting flashes may work. Determining faults and repair procedures differ from manufacturer to manufacturer and there are way too many to break down into one article. My advice, read up on that particular manufacturers systems that you will be dealing with and learn everything there is to know about that system works.
For me, it’s the scanners that make the difference. I have several dealer level and aftermarket scanners for working with air bag systems. Some of the scanners are dedicated to only certain models air bag systems, European, Asian, etc… They can be expensive and you’ll have to weigh the cost of these scanners vs. how much use you’ll get from them. The one problem I find with the dedicated air bag scanners is the get dated extremely fast. A lot of times the manufacturer has no updates available for them and whatever years and models they cover is it, and as the years pass by the dust settles on the scanners case never to be opened again, seriously. So think about it before you buy a scanner for that purpose. Since I do a lot of business with several body shops I can weigh the cost with the amount of work that I get from them. Without those jobs, I wouldn’t believe it would be a paying proposition.
However, as time has a way of changing things, so does the scanning capabilities. There are some great aftermarket companies out there with some outstanding equipment and information available to the independent marketplace. Which should help making the decision on which type of equipment to purchase.
Along with knowing the airbag systems you will also need to brush up on your skills dealing with different interior components. Everything from removing the driver’s airbag (special tools maybe required) to removing the dash panels for access to the passenger airbags. I’ve even had to replace entire dash panels because the passenger air bag is built into it and not separate. It seems pretty silly to change an entire dash panel because of it, but I only repair the problems, I’m the design engineer. (I hope their reading this… What? You couldn’t design it separately? Seems like a huge waste of material guys.)
You’ll also need to work on your upholstery skills. Oh yes, because a lot of manufacturers have installed the side impact bags into the seats themselves. Now you’ll have to pull the seat out, break it down to the foam and frame to replace that air bag. Let’s not forget about the headliners and seat belt systems. The seat belt system is as much a part of the air bag systems as the air bags themselves. Seat belts in the early days of air bags were not a part of the system but after many years of testing and development the seat belt has become an integral part of the overall safety systems in today’s vehicles.
Adding even more to the diagnostics and repair part of the airbag systems is the "Passenger Presence System" (PPS) or on some vehicles referred to as the Occupant Presence System or the Occupant Classification System. For the most part they are basically the same thing. It is a required reprogram for those vehicles equipped with the system. On some of the manufacturers you'll need certian pre-shaped weights that you place on the passenger seat in order to correctly "zero" or recalibrate the unit. This reprogramming gives the controller the ability to detect whether it's a child seat or a full size adult occupying the seat. If the contol module doesn't "sense" any weight then it will not command the passenger air bag to engage. (On some vehicles it uses the weight as a way of determining speed of the passenger airbag deployment.) Failure to program the PPS will leave the airbag light on.
The airbag systems are here to stay, and with more and more people losing touch with what makes their mode of transportation run down the road, the more the manufacturer wants to keep that proverbial complaisant driver from hurting themselves or their passengers in a collision. We have the engineering these days to do just that, and the future of passenger compartment protection is looking even better.
These days, as automotive technician… you’re not just the guy who keeps a customer’s car tuned-up and running great… but you’re also the person that can help keep them safe on the open road and possibly save a life or two.