performs calculations using the measured accelerations. The SDM 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 air bags. Once
the air bags are inflated they quickly deflate through the air bag vent holes. After the air bags
have deployed, the SDM sets a diagnostic trouble code (DTC) and requests the IPC to turn the
AIR BAG indicator ON. The SDM, instrument panel (I/P) module, steering wheel module,
steering wheel module coil and the connecting wires makeup the frontal deployment loops. The
SDM continuously monitors the deployment loops for malfunctions and requests the IPC to turn
the AIR BAG indicator ON if a fault is detected.
Side SIR System Description (Front)
The side Supplemental Inflatable Restraint (SIR) System (front) consists of the following
components:
AIR BAG indicator located in the instrument panel cluster (IPC)
Inflatable restraint roof rail modules front/rear, (left/right)
Inflatable restraint sensing and diagnostic module (SDM)
Inflatable restraint side impact sensors (SIS) (left/right)
Inflatable restraint vehicle rollover sensor
Inflatable restraint wiring harnesses
Seat belt pretensioners (left/right)
The roof rail modules (front/rear) are located in the headliner along the roof rails. The roof rail
modules contain a housing, inflatable air bag, initiating device, and a canister of gas generating
material. The initiator is part of the roof rail 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 roof rail air bag. The SDM, roof rail modules (front) and the connecting wires
makeup the side deployment loops. The SDM continuously monitors the deployment loops for
malfunctions and turns the AIR BAG indicator ON if a fault is present. Each roof rail module is
equipped with a shorting bar located on the connector of the module. The shorting bar shorts the
roof rail module deployment loop circuitry to prevent unwanted deployment of the air bag when
servicing the inflator module.
Inflatable Restraint Sensing and Diagnostic Module (SDM)
The sensing and diagnostic module (SDM) is a microprocessor and the control center for the
Supplemental Inflatable Restraint (SIR) System. The SDM contains internal sensors along with
2008 Chevrolet Silverado 1500
2008 RESTRAINTS Supplemental Inflatable Restraints - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado