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This
material first appeared in the I-CAR Advantage Online, which is published and
distributed free of charge. I-CAR, the Inter-Industry Conference on Auto
Collision Repair, is a not-for-profit international training organization that
researches and develops quality technical education programs related to
collision repair. To learn more about I-CAR, and to subscribe to the free
publication, visit
www.i-car.com.
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Airbags
When working on a collision-damaged vehicle there
is often a risk factor involving undeployed airbags. Simply disconnecting the
battery does not eliminate that risk. Late model vehicles can have airbags in
several locations.
When front driver airbags were first developed,
the main inflator propellant used was sodium azide. With these types of
inflators, an electrical signal causes the pellets to begin burning, creating
nitrogen gas, which deploys and inflates the airbag. Sodium azide was also the
propellant for the first front passenger airbags.
Today, many airbags are deployed by compressed gas
cylinders. A compressed gas inflator operates by sending an electrical signal
from the restraint system control module to a small disk (performing a function
similar to a soda bottle cap) on the gas inflator. The disk burns and the
escaping compressed gas inflates the airbag. Compressed gas cylinders may be
stored in a compressed state upwards of 435 kPa (3,000 psi). Puncturing the
cylinder will cause a high burst of high-pressure gas that could result in
flying metal, plastic, or glass. This can occur even if the airbag system is
disabled.
One of the reasons for choosing compressed gas as
a propellant is the space restriction where these airbags are located. The
compressed gas inflators are the shape of a long cylinder. With this design, the
inflator can be positioned inside the instrument panel, seat back, door panel,
or along any rail or pillar of the vehicle. Another concern with sodium azide is
heat. When sodium azide burns, it generates a great amount of heat. If located
in the soft trim areas of a vehicle, fires may be caused by airbag deployment.
Compressed gas allows airbag deployment temperatures to be kept lower.
Front airbags are located in the steering wheel
for the driver and the passenger-side instrument panel for the passenger. Side
airbags are located either in the doors, seat backs, or pillars. Side curtain
airbags are dropped down from the headliner along the roof rail. Knee airbags
deploy from the knee bolster.
If it is necessary to remove an undeployed airbag,
it should be deactivated. To deactivate and remove an airbag module and
inflator, the 12-volt electrical system of the vehicle must be de-energized by
following the vehicle maker’s specific procedures. Not all passive restraint
systems de-energize the same. Depending on the discharge rate of the capacitors
used within the system, they may discharge as fast as 30 seconds or it make take
a number of minutes before airbag removal can safely occur.
Deactivating an airbag assembly or even
disconnecting the airbag connectors does not eliminate the risk of deployment.
Since only a small amount of current is required to activate an airbag circuit,
static electricity could still deploy an airbag. The best way to avoid static
electricity build-up is to handle the airbag like a computer module. Ground
yourself with an anti-static discharge strap, attaching the strap to vehicle
ground. Once the airbag is out of the vehicle, remove the wrist strap and carry
the airbag so that it would deploy away from your body.
When removing and installing a seat, the
technician or the seat should be grounded to prevent static electricity from
deploying the airbag. Do not hold the seat with your hands over the undeployed
side airbag, and carry the seat so that the undeployed airbag is away from your
body.
Hold an undeployed side curtain airbag so that if
deployed, it would fold out or downward, not toward you.
The undeployed airbag, or seat, should be stored
in a safe location where it is not subjected to conditions that could cause an
airbag module to deploy, such as stray voltage or static electricity.
The driver and passenger airbag have the potential
to be a dual-stage design. This means that even though the airbag is deployed,
there may still be a live charge inside the airbag module that could be
deployed.
For technicians, two ways to identify if an airbag
is a two-stage design is to refer to the vehicle maker service manual or when
the airbag is removed, look for two wire connectors attached to the airbag
module. All dual-stage airbags have two connectors, and single stage airbags
have one connector going to the airbag module assembly.
Restraint System Wiring Repairs
Confusion exists concerning the repair of some
damaged wiring and wiring connectors for restraint systems. The perception is
that restraint system wiring should never be repaired. While it is true that
some vehicle makers do not recommend the repair of wiring and connectors for the
restraints system, others have very detailed printed procedures and even offer
repair kits expressly for the repair of restraint system wiring. Repairing
damaged restraint system wiring, when applicable and the parts and procedures
are available, can save unnecessary replacement of the main body and instrument
panel wiring harnesses.
As an example, we will focus on the repair of
restraint system wiring on US market General Motors (GM) vehicles. Whenever
doing restraint system wiring repairs, always follow the procedures and use the
parts and equipment specified by the vehicle maker for the vehicle being
repaired. This information can be found typically in the “BODY” section of the
service information under “WIRING REPAIR” for GM vehicles.
Let’s begin with some background on how the
self-diagnostic capabilities of modern restraint systems function. When a
problem exists in the electrical circuit of a restraint system, a diagnostic
trouble code (DTC) is stored in the restraint system control module and a
malfunction indicator lamp (MIL), or airbag warning lamp, on the instrument
panel is turned on to alert the driver.
The computer is able to detect problems by
monitoring system voltage, amperage, and resistance readings, and comparing them
to specified values. If a monitored value falls outside the programmed
parameters, a DTC is set and the MIL is turned on. Wiring repairs done
improperly can increase the resistance in a circuit to the point that the
control module senses a fault and sets a DTC. Repairs that do not completely
seal the splice joint from moisture can allow corrosion of the connection. This
corrosion will also increase circuit resistance and eventually lead to a DTC and
MIL.
What makes a restraint system wiring repair
different from any other wiring repair? While there are a couple of
recommendations that may be specific to restraint systems, the reality is that
restraint system wiring repair demands the same best practices that should be
observed with any other wiring repair. The first, and maybe only real
difference, is that while GM recommends repairs rather than the replacement of a
wiring harness, short pigtails that are attached to parts such as sensors and
inflator modules are not repairable. If a pigtail connected to a part is
damaged, the part should be replaced.
Restraint system wiring repairs vary from a simple
splice of a cleanly cut wire or replacement of sections of damaged wire, to
replacement of terminals or even entire connectors. All of these operations may
involve splicing wires together.
To help address the issue of making low resistance
and moisture-proof, or air-tight splices, special “DuraSeal” crimp and seal
splice sleeves were designed (pictured). These connectors differ from the
conventional butt connectors in a couple of important ways.
First, they have a special cross-hatched (knurled)
core crimp barrel that provides the necessary contact integrity to make a low
resistance splice. Secondly, they have a special heat shrink sleeve that
contains a sealing adhesive inside. When the connectors are heated, they shrink
over the wire and make an air-tight seal that protects the connection from the
environment. Although these connectors were initially designed for repairing
restraint system wiring, because of their superior performance, they are now the
recommended splice by GM for all wiring repairs. The only limitation these
connectors have is that they can only be used to splice two wires together. For
repairs to original equipment splices of three or more wires, special splice
clips are available from GM. These types of connections are typically limited to
grounds and their application to restraint system wiring is not common. The
splice clips have detailed instructions included for applications and usage.
The splice sleeves are available in different
sizes and are colour coded. Green coloured splices (88988379) are used for 22-24
gauge, salmon (#12089189) for 18-20 gauge, blue (12089190) for 14-16 gauge, and
yellow (12089191) for 10-12 gauge. To ensure circuit integrity the correct
splice sleeve for the wire size must be used.
The tools and procedures used when making wire
splices is as important as the type of splice connector. If the crimping tool
used on the connector damages the insulation tubing over the metal core crimp
barrel, the connection may not be sealed sufficiently from moisture, resulting
in corrosion. Because of this, GM recommends a special splice crimping tool
(J-38125-8, GM P/N 12085115) be used (pictured).
The crimping tool has three nest positions.
Position 1 is used for 18-24 gauge wire, or the green and salmon coloured splice
sleeves. Position 2 is for 14-16 gauge wire, or the blue splice sleeves, and
position 3 is for 10-12 gauge wire, or the yellow splice sleeves. The nest
positions on the crimp tool are colour-coded for easy reference. The crimping
tool also has a locking ratchet mechanism in the handle that keeps the tool from
being reopened until the proper amount of pressure has been applied to the
splice sleeve. After the splice sleeve has been put into the proper nest, and
the wire inserted into the metal core crimp, the handles on the crimping tool
are closed and squeezed until they open when released. This ensures that just
the right amount of pressure is applied to the splice sleeve.
To repair damage to GM restraint system wiring,
follow this procedure.
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Open the wiring harness by removing any tape. Do
not damage the wiring insulation when cutting the harness open. A sewing ripper
works well for this.
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Cut as little wire off the harness as possible.
Damaged sections of wire must be removed and other sections may need to be cut
away to change the locations of splices. Splices should be located at least 40
mm (1.5 in) away from harness branches, connectors, or other splices.
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Strip the insulation from the splice locations.
You must obtain a clean strip with all of the wire strands intact. If you are
unsure of the wire size, and have no way to accurately measure it, begin with
the largest opening on the wire stripper and work down until a clean strip of
the insulation is achieved. Strip about 7.5 mm (5/16 in) of insulation from each
wire to be spliced. After stripping the wire, inspect the wire strands for nicks
or cut strands. If any damage is found to the wire, cut the damaged portion off
and repeat the stripping procedure.
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Select the proper size splice sleeve for the wire
size.
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Obtain the correct splice crimp tool to crimp the
splice sleeve.
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Place the splice sleeve in the correct nest of the
crimping tool. Ensure that the crimp made falls midway between the end of the
metal crimp barrel and the wire stop. The wire stop is in the centre of the
barrel. Close the crimping tool handles slightly in order to firmly hold the
splice sleeve in the crimp tool nest.
-
Insert the wire into the splice sleeve barrel
until the wire hits the stop.
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Tightly close the crimping tool handles until they
open when released.
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Repeat steps 6-8 for the opposite end of the
splice sleeve.
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Using a heat torch (J-38125-5 or equivalent),
apply heat to the crimped area of the barrel. Gradually move the heat to the
open end of the splice sleeve tubing. The shrink tubing will shrink down tightly
against the wire as the heat is applied, and a small amount of sealant will come
out of the open end of the tubing. The heat torch used should have a heating
barrel to distribute the heat evenly around the entire splice
sleeve.
Damaged connector terminals present other
considerations. The terminals are gold plated to ensure the contact integrity of
the sensitive low energy restraint system circuit. Damaged terminals in the
sensing and diagnostic module (SDM) harness connector can be replaced, but must
only be replaced with the terminated leads in the SIR/SRS connector repair
assembly pack. Do not substitute any other terminals for those in the SIR/SRS
assembly packs. These terminals are crimped onto short sections of wire that can
be spliced into the harness with the splice sleeves after they are inserted into
the connector body. Damaged terminals in other restraint system connectors are
repaired by splicing a new connector assembly into the wiring harness. The
wiring harness side connectors are available as service parts.
When sections of wire require replacement, ensure
that the wire used is the same wire size and type as that being replaced. Other
parts that are available for restraint system wiring repairs include connector
position assurance (CPA) inserts and terminal position assurance (TPA) inserts
(pictured). The CPAs are inserted through locking tabs on the connectors to
ensure that the connector halves cannot vibrate apart, and the TPAs keep the
terminal pins seated securely in the connector body. Both of these inserts must
be undamaged and in place to ensure good contact between the mating terminals of
the connection.
All of these parts are available separately or in
an SIR Repair Kit tray. The SIR tray is a part of a bigger Terminal Repair Kit
(J-38125) that includes all the tools, connectors, splice sleeves, and other
parts to repair any part of a damaged wiring harness. Also included in the SIR
Repair Kit tray is shrink tubing that is used to cover splices and protect them
from heat in areas where they are exposed to high temperatures. Yellow
electrical tape is supplied so that colour coding of the wiring can be
maintained for splices made in areas that have colour-coded wiring.
Restraint system wiring repairs are allowed by
several vehicle makers, including GM. While not difficult, always follow the
vehicle maker’s recommendations as to the parts and procedures used. This will
ensure that the integrity of the system is maintained and that repairs will have
the durability necessary to maintain proper system functioning.
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