SIR System Overview
The supplemental inflatable restraint (SIR) system supplements the protection
offered by the occupant seat belt system (2). The SIR system has various inflator
modules located throughout the vehicle, i.e. inflatable restraint steering wheel
module (1), inflatable restraint I/P module (1), and the inflatable restraint
side impact module - LF. Each inflator module has a deployment loop that
is controlled by the inflatable restraint sensing and diagnostic module (SDM),
which is mounted inside of the vehicle. The SDM performs continuous diagnostic
monitoring of the SIR system electrical components. Upon detection of a circuit
malfunction, the SDM will set a diagnostic trouble (DTC) and inform the driver
by commanding the instrument panel cluster (IPC) to turn the AIR BAG indicator
ON. The steering column and knee bolsters (3) are designed to absorb energy
and compress during frontal collisions in order to limit leg movement and decrease
the chance of injury to the driver and front passenger.
Frontal SIR System Description
The frontal SIR system consists of the following components:
• | AIR BAG indicator in the instrument panel cluster (IPC) |
• | Driver and front passenger knee bolsters |
• | Inflatable restraint instrument panel (I/P) module |
• | Inflatable restraint sensing and diagnostic module (SDM) |
• | Inflatable restraint steering wheel module |
• | Inflatable restraint steering wheel module coil |
A frontal collision of sufficient force will deploy the frontal inflator modules.
The SDM contains a sensing device (accelerometer) that converts vehicle velocity
changes to an electrical signal. The SDM contains a microprocessor, which performs
calculations using the measured accelerations and compares these calculations
to a value stored in memory. When the generated calculations exceed the stored
value, the SDM will cause current to flow through the frontal deployment loops,
deploying the frontal inflator modules. Once the inflator modules are inflated,
they quickly deflate through the air bag vent holes and/or the bag fabric. After
the inflator modules are deployed, the SDM sets a deployment commanded DTC and
then commands the IPC to turn the AIR BAG indicator ON. The SDM, I/P
module, steering wheel module, steering wheel module coil and the connecting wires
make up the frontal deployment loops. The SDM continuously monitors the deployment
loops for malfunctions and commands the IPC to turn the AIR BAG indicator ON
if a fault is detected.
Inflatable Restraint Sensing and Diagnostic Module (SDM)
The inflatable restraint sensing and diagnostic module (SDM) is a microprocessor
and the control center for the SIR system. The SDM contains internal sensors
along with external sensors, if equipped, mounted at various locations, depending
on vehicle. In the event of a collision, the SDM performs calculations using
the signals received from the internal and external sensors, if equipped.
The SDM compares the result of the calculations to values stored in memory.
When these calculations exceed the stored value, the SDM will cause current
to flow through the deployment loops, deploying the inflator modules. The SDM
records the SIR system status when a deployment occurs and commands the IPC
to turn the AIR BAG indicator ON. The SDM performs continuous diagnostic monitoring
of the SIR system electrical components and circuitry when the ignition is ON.
If the SDM detects a malfunction, a DTC will be stored and the SDM will turn
the AIR BAG indicator ON. In the event that ignition 1 voltage is lost
during a collision, the SDM maintains a 36 volt loop reserve (36 VLR)
for deployment of the inflator modules. It is important to note, when disabling
the SIR system for service or rescue operations, to allow the 36 VLR
to dissipate, which could take up to 1 minute.
AIR BAG Indicator
The AIR BAG indicator, located in the IPC is used to notify the driver of SIR
system malfunctions and to verify that the SDM is communicating with the IPC.
When the ignition is turned ON, the SDM and the IPC are supplied with ignition 1
voltage. The IPC responds by flashing the AIR BAG indicator seven times. While
the IPC is flashing the AIR BAG indicator, the SDM conducts tests on all SIR system
components and circuits. If no malfunctions are detected, the SDM will command
the IPC to turn the AIR BAG indicator OFF via Class 2 serial data. The
SDM provides continuous monitoring of the inflator module circuits by conducting
a sequence of checks. If a malfunction is detected, the SDM will store a diagnostic
trouble code (DTC) and command the IPC to turn the AIR BAG indicator ON via
Class 2 serial data. The presence of a SIR system malfunction could result
in non-deployment of the inflator modules. The AIR BAG indicator will remain
ON until the malfunction has been repaired.
The AIR BAG indicator is the key to driver notification of SIR system malfunctions.
The AIR BAG indicator is used to inform the driver of the proper operation of
the SIR system. The SDM uses the AIR BAG indicator to do the following:
• | Verify proper SIR system operation by commanding the AIR BAG indicator
OFF via Class 2 serial data. |
• | Warn the driver of SIR system malfunctions, which could potentially result
in one or more of the following conditions: |
- | Deployment of the frontal inflator module(s) without a frontal crash; |
- | Deployment of the side impact inflator module(s) without a side crash; |
- | Non-deployment of the frontal inflator module(s) in the event of a crash; |
- | Non-deployment of a side impact inflator module in the event of a side
crash; or |
- | Deployment of an inflator module(s) for conditions less severe than intended. |
Inflator Modules
The inflator modules consist of a housing, an inflatable air bag, the initiator,
a canister of gas generating materials, and in some cases, stored compressed gas.
The initiator is part of the inflator module deployment loop. When the vehicle
is involved in a collision of sufficient force, the SDM causes current to flow
through the deployment loops to the initiator. Current passing through the initiator
ignites the material in the canister producing a rapid generation of gas and
the release of compressed gas, if present. The gas produced from this reaction
rapidly inflates the inflator module. Once the inflator module is inflated,
it quickly deflates through the vent holes and/or the fabric. Each inflator
module is equipped with a shorting bar that is located in the connector of
the inflator module. The shorting bar shorts the inflator modules circuitry
to prevent unwanted deployment of the inflator module when the connector is
disconnected.
Inflatable Restraint Steering Wheel Module Coil
The steering wheel module coil is attached to the steering column and is located
under the steering wheel. The steering wheel module coil consists of 2 or
more current - carrying coils. The coils allow the rotation of the steering
wheel while maintaining continuous electrical contact between the steering wheel
module deployment loop and the steering wheel module. Two coil wires are used
for the steering wheel module deployment loop. Additional coil wires are used
for accessories that are attached to the steering wheel, depending on the vehicle
model. The steering wheel module coil connector is located near the base of
the steering column. The connector contains a shorting bar that shorts the steering
wheel module coil deployment loop circuitry to prevent unwanted deployment
of the steering wheel module when the connector is disconnected.
Side SIR System Description
The side impact SIR system consists of the following components:
• | Inflatable restraint sensing and diagnostic module (SDM) |
• | Inflatable restraint side impact modules - LF |
• | inflatable restraint side impact sensors (SIS) - LH |
• | AIR BAG indicator in the instrument panel cluster (IPC) |
The side impact modules are located in the outside portion for the front seat
backs. The side impact modules contain a housing, inflatable air bag, initiating
device, and a canister of gas generating material. The initiator is part of the
side impact module deployment loop. When a side impact of sufficient force occurs,
the SIS detects the impact and sends a signal to the SDM. The SDM compares the
signal received from the SIS to a value stored in memory. When the generated signal
exceeds the stored value, the SDM will cause current to flow through the side
deployment loop, deploying the inflator module. The SDM, side impact modules and
the connecting wires make up the side deployment loops. The SDM continuously monitors
the side deployment loops for malfunctions and commands the IPC to turn the AIR
BAG indicator ON if a fault is present.
Inflatable Restraint Side Impact Sensor (SIS)
The side impact sensors (SIS) contains a sensing device (accelerometer) which
monitors vehicle acceleration and velocity changes to detect side collisions that
are severe enough to warrant side inflator module deployment. The SIS is not part
of the deployment loop, but instead provides an input to the SDM. The SDM contains
a microprocessor that performs calculations using the measured accelerations and
compares these calculations to a value stored in memory. When the generated calculations
exceed the stored value, the SDM will cause current to flow through the deployment
loops, deploying the side inflator module(s).
Inflatable Restraint Wiring Harness
The inflatable restraint wiring harness connects the inflator modules, the SDM,
the deployment loops, and the serial data circuit together using weather - packed
connectors. SIR system connectors are yellow for easy identification. When repairing
SIR wiring harnesses, follow the proper testing and repair procedures listed
in the service manual.
Steering Wheel and Column
The steering wheel and column are designed to absorb energy when driver contact
is made with steering wheel or inflated module. In a collision, the driver may
contact the steering wheel directly or load the steering wheel and column through
the inflated module. When the driver applies load to the inflator module or
the steering wheel, the column will compress downward, absorbing some of the
impact and helping to reduce bodily injuries to the driver. The steering wheel
and column must be inspected for damages after a collision.
Knee Bolster
The knee bolsters are designed to help restrain the lower torso of front seat
occupants by absorbing the energy through the front seat occupant's upper legs.
In a collision, the front seat occupant's legs may come in contact with the knee
bolsters. The knee bolsters are designed to crush and deform, absorbing some of
the impact and helping to reduce bodily injuries. The driver and passenger knee
bolsters are located in the lower part of the instrument panel and must be inspected
for damages after a collision.