The last decade of consumer awareness has introduced many service
facilities to a new standard of performance. Among the technological
advancements pushing this new standard higher and higher are new
supplemental safety systems, which command a thorough understanding
of system operations as well as troubleshooting procedures that
must be strictly adhered to by everyone involved in the repair.
Since the first air bags – called supplemental inflatable restraint
systems (SIRS) – were introduced, increasingly complex systems
with added deployment loops have been produced. These newer systems
not only take measures to ensure actuation, control and diagnosis
of the air bag itself, but also provide for the same system’s
function in regard to auxiliary systems indirectly tied to an
actual air-bag deployment – for example, an adaptive restraint
system that would automatically tension the harness for shoulder
The United States is the only country in the world that compels
vehicle manufacturers to offer air bags as standard equipment
on all new passenger cars and light trucks. This regulatory pressure,
in conjunction with consumer interest in safety, has led to 60
million vehicles with air bags to be sold in the United States
To prepare you for the new standard of SIRS repair, I’ll cover
some components and systems currently in service, as well as some
that soon will be.
The Impact of Side Air Bags
Side-impact air bags are available on several makes of European
cars, but the systems in use have only a short track record, according
to Sam Decker, an insurance claims agent (adjuster) for Southwest
Missouri. The side-impact air bag typically catches "loose
end" types of major incidents, says Decker, but in a few
cases, he’s had customers asking questions such as, "Why
didn’t the bag deploy if the car slid into a ditch sideways?"
With that concern in mind, I spoke with representatives from Mercedes-Benz
– which has had side-impact air bags installed in its "S"
Class vehicles since 1985 and recently equipped all of its ’98
cars with them. Their response: Triggering sensors are the biggest
challenge. Since the doors offer less collapsible area than the
front body structure, there’s only a fraction of the time available
to sense and deploy the bag in an accident. In an attempt to overcome
this, Mercedes developed a "satellite sensor." This
hardware links the central triggering unit located in the center
of the vehicle to two alternate sensors located at the outer seat
lines on the seat cross-members. These sensors register impact
readings, as well as severity, before relaying a signal to deploy
the air bag. A timeline of approximately 7 milliseconds is all
that’s available for this routine. Decision making aside, the
bag is fully deployed in 20 milliseconds.
As to why certain collision events don’t project a profile for
air-bag deployment, Mercedes representatives say the manufacturer
builds in a safety factor that discriminates against "misuse"
incidents, which are then screened out by the system. "Misuse"
incidents include such things as kicks, hammer blows, simulated
collisions with bicycles and similar occurrences.
Researching this further, I came upon several of the latest domestic
advances and new developments, including a new piece of technology
being developed by Delphi Corporation of Delco Electronic Systems.
Called the "Bumped I.C. Single Chip," this marvel of
technology is based on signal processing circuitry that boosts
the signal of an accelerometer signal by 250. This signal gain
is supposed to work with an analog/digital algorithm developed
specifically for side-impact crashes. Current technology is available
for production of the chip, and diagnostics can be added to mainstream
SIRS components without a problem.
New developments in SIRS – Mercedes-Benz’s soon-to-be-produced
infant-seat tagging system for example – can seem intimidating
at first. The philosophy behind such systems involves the detection
of a resonator unit or a tag identifier placed in a critical area.
In most cases, the tag is affixed to a rear-facing infant seat
– a special car seat is required – in the front passenger seat.
The transponder can transmit a code that inhibits the passenger
air bag from deploying. Dubbed "Baby Smart™" by
Mercedes, the system’s concept is currently being developed by
other auto manufacturers as well. An important consideration is
the complete immunity to other scan-rescan sources; the price
of such a compromise should also include a diagnostic format.
Self-diagnostic capability is built into this gear, but it requires
encoding to prevent unauthorized scan programing errors that could
render the system useless.
Along with the advanced logistical technology of a workable infant-seat
tagging system, it seems that a weight-based seat/sensor linked
system – designed for lightweight, smaller individuals not currently
addressed in other passive safety systems – might soon appear.
By using a direct weight measurement, not a pattern or redundant
threshold, such a system could suppress the passenger-side air-bag
function when, for instance, a small child is sitting in the front
Other important developments in SIRS technology include:
- Microprocessor-based, hybrid-designed crash detectors with
the capability to sense varying degrees of crash severity. Multistage
air-bag development (currently on hold) would be the most logical
pairing of such a crash sensor.
- The side-impact satellite (SIS) developed by the Delco/Delphi
Division of General Motors is designed to sense and discriminate
crash pulses, sorting out the ones that require actual air-bag
deployment. Delphi claims the SIS has ultra-immunity to "misuse"
events, such as shopping carts that slam into a car door and other
nonhazardous events, but can accurately identify a real-world
accident. Mounting of an SIS will be in the B-pillar, inner door
sheet metal or the side rail.
- According to many sources, sensing and diagnostic modules
will comprise the greatest improvements in SIRS technology in
the next decade. The ability to use multiple pyrotechnic loops
means that one controller can deploy one or all air bags in a
common or estranged loop. Cost-effective measures such as this
may make it possible to include SIRS in most heavy-duty equipment,
including off-road designs. Multiple configurations are also making
it possible for countries not currently developing systems of
their own to buy these systems and fit them for OE or retrofits
on new and late-model vehicles in their respective countries.
The Impact on Body Shops
Long Beach Auto Body in Southern Missouri performs vehicle restorations
on a lot of hard crashes, says owner and operator Randy Johnson,
who sends out air-bag renewal to specific dealers and depends
on them for troubleshooting and disposal at the local level. Long
Beach Auto Body, I discovered, is typical of small or rural area
shops that don’t wish to invest heavily in scan tools or other
specialized test equipment in a rapidly changing area of technology.
The reprogramming of PCM units can be a big problem for those
shops trying to perform their own internal air-bag repairs, says
Johnson. Manufacturers are constantly updating, and programming
criteria may change from day to day.
Larry Warren of Warren Auto-Works in Springfield, Mo., told me
he initially climbed on the SIRS bandwagon, buying all the books
and tools, and enrolling in all the training courses. These days,
Warren says he farms out most air-bag work because of potential
liability and extreme customer concern. When a job involves the
repair of an air bag, Warren keeps the vehicle’s air-bag repair
invoice on file as protection.
When it comes to estimating a vehicle’s damage, Warren supplies
insurance companies estimates based upon his own inspection and
then allows room for expert assistance or leaves the estimate
open for SIRS repairs and follow-up.
Other shop owners across the country do, indeed, repair, recertify
and maintain diagnostic capability regarding air-bag systems.
The majority of those I spoke with allowed for a workflow that
included a preliminary look at a deployed system and then an estimate
based on replacing every element in the system. The reason, says
shop owner David Huey of City Carriage Auto and Paint in Trinidad,
Colo., is because system reactivation isn’t a sure thing, and
clearing lights, as well as complying with manufacturer test procedures,
sometimes makes replacing a part the only prudent thing to do.
Huey remembers a ’96 Chevy Cavalier that deployed the passenger
air bag to an empty occupant position when the car ran over a
large rock. In such a case, the deployment loop was certainly
suspect, and since the bag ripped off the rear view mirror, collapsed
the windshield and literally wrecked the entire dashboard, Huey
ran this one by a dealership for "confirmation of integrity"
after it was
From personal experience, I’m aware that OEM dealers do a great
deal of air-bag work for the aftermarket at both the mechanical
and body repair levels. Another source contacted confirmed that
this trend is widespread. David Goldsmith, service manager for
a General Motors dealership in Branson, Mo., says the dealership’s
typical air-bag refurbishment customers are smaller shops with
less than three employees. And that trend will probably continue.
Special tools are already a must in most repairs involving deployed
air bags, says Goldsmith, and because new, advanced controllers
will be employed in the future, repairs will only get more complex.
What’s It All About?
Remember seat belts, inertia reels and the infamous mandatory
interlocks of the ’70s? They were a big deal back then, and today,
they still play an important role. The latest technological advances
– like supplemental inflatable restraint systems, infant-seat
tagging systems and side-impact satellites – developed to save
motorists lives wouldn’t be as developed as they are if it hadn’t
been for the early accomplishments.
Who knows what the future really holds for SIRS. Sources close
to research and design for at least one Asian car maker told me
that roll-over SIRS protection packages may be available very
soon from Japanese manufacturers. U.S. car makers are also currently
working on this
Whatever advances the future brings, it’s important for technicians
to fully understand the various systems and their components.
It’s also important to recognize your shop’s repair limitations.
Supplemental inflatable restraint systems were developed to protect
the occupants of a vehicle involved in a collision. Therefore,
by being sure the work you perform on any air-bag system doesn’t
compromise its integrity, you can also rest assured of your impact
on the safety of motorists everywhere.
Writer Bob Leone, a retired shop owner, is ASE Three-Way Master
Certified and is completing qualifications as a post-secondary
automotive instructor in the vocational school system in Missouri.