Hummer H2. Manual - part 2054

The frontal SIR system consists of the following components:

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AIR BAG indicator located in the instrument panel cluster (IPC)  

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Driver and passenger knee bolsters  

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Inflatable restraint electronic frontal sensors (EFS) (left/right)  

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Inflatable restraint I/P module.  

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Inflatable restraint I/P module disable switch  

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Inflatable restraint I/P module disable switch indicator  

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Inflatable restraint sensing and diagnostic module (SDM)  

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Inflatable restraint steering wheel module  

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Inflatable restraint steering wheel module coil  

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Inflatable restraint wiring harnesses  

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Steering wheel and column  

A frontal collision of sufficient force will deploy the frontal air bags. The SDM contains a sensing device that 
converts vehicle velocity changes to an electrical signal. In the event of a frontal collision, the SDM receives a 
signal from the electronic frontal sensors which assists the SDM in determining the severity of some frontal 
collisions. The SDM contains a microprocessor that 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 instrument panel cluster (IPC) to turn 
the AIR BAG indicator ON. The SDM, 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 turns the AIR BAG indicator ON if a fault is detected. 

Inflatable Restraint Sensing and Diagnostic Module (SDM) 

The sensing and diagnostic module (SDM) is a microprocessor and the control center for the SIR system. The 
SDM contains internal sensors along with several external sensors, if equipped, mounted at various locations on 
the vehicle. In the event of a collision, the SDM performs calculations using the signals received from the 
internal and external sensors. The SDM compares the results of the calculations to values stored in memory. 
When these calculations exceed the stored value, the SDM will cause current to flow through the appropriate 
deployment loops to deploy the air bags. The SDM records the SIR system status when a deployment occurs 
and requests the instrument panel cluster (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 
turned ON. If the SDM detects a malfunction, a DTC will be stored and the SDM will command the AIR BAG 
indicator ON. In the event that ignition 1 voltage is lost during a collision, the SDM maintains a 23-volt loop 
reserve (23 VLR) for deployment of the air bags. It is important to note, when disabling the SIR system for 
servicing or rescue operations to allow the 23 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 is supplied with 

 

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ignition 1 voltage and requests the IPC to flash the AIR BAG indicator 7 times. While flashing the indicator, the 
SDM conducts test on all SIR system components and circuits. If no malfunctions are detected the SDM will 
communicate with the IPC through the class 2 serial data circuit and request the IPC to turn the AIR BAG 
indicator OFF. The SDM provides continuous monitoring of the air bag circuits by conducting a sequence of 
checks. If a malfunction is detected the SDM will store a diagnostic trouble code (DTC) and request the IPC to 
turn the AIR BAG indicator ON. The presence of a SIR system malfunction could result in non-deployment of 
the air bags. The AIR BAG indicator will remain ON until the malfunction has been repaired. 

Inflator Modules 

The inflator modules contain a housing, inflatable air bag, an initiating device, canister of gas generating 
material 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 will cause 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 air bag. Once the air bag is inflated it quickly deflates through the air bag vent holes 
and/or the bag fabric. 

Each inflator module is equipped with a shorting bar located on the connector of the module. The shorting bar 
shorts the inflator module deployment loop circuitry to prevent unwanted deployment of the air bag when 
servicing the inflator module. 

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 two or more current-carrying coils. The coils allow the rotation of the 
steering wheel while maintaining continuous electrical contact between the driver deployment loop and the 
steering wheel module. Four coil wires are used for the steering wheel module deployment loop. Additional coil 
wires are used for accessories 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 
air bag when it is disconnected. 

Inflatable Restraint Electronic Frontal Sensor (EFS) 

The electronic frontal sensors (EFS) are equipped on vehicles to supplement the SIR system performance. The 
EFS is an electronic sensor and is not part of the deployment loops, but instead provides an input to the SDM. 
The EFS can assist in determining the severity of some frontal collisions. The SDM uses the input from the 
discriminating sensor to assist in determining the severity of a frontal collision further supporting air bag 
deployment. If the SDM determines a deployment is warranted, the SDM will cause current to flow through the 
deployment loops deploying the frontal air bags. 

Inflatable Restraint I/P Module Disable Switch 

The instrument panel (I/P) module disable switch is a manual 2-position key switch located inside the vehicle. 
The I/P module disable switch allows the vehicle operator the ability to enable or disable the I/P module 
(passenger frontal air bag). The vehicle operator must disable the I/P module if a rear-facing child seat is 
installed in the front passenger seat. The I/P module disable switch interfaces with the sensing and diagnostic 

 

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module (SDM) to request the enabling or disabling of the I/P module. The occupants are notified of the 
enabling or disabling of the I/P module via the I/P module disable switch ON/OFF indicator located in the I/P 
module disable switch. 

Inflatable Restraint I/P Module Disable Switch Indicator 

The instrument panel (I/P) module disable switch ON/OFF indicator is an LED located in a position that can be 
viewed by the occupants in the front seats. The location varies depending on the vehicle. When the I/P module 
disable switch is in the disable position, the I/P module disable switch indicator illuminates. When the I/P 
module disable switch is in the enable position, the I/P module disable switch indicator is not illuminated. The 
I/P module disable switch indicator will dim to a lower intensity when the headlamp switch is turned ON. 

Inflatable Restraint Wiring Harnesses 

The inflatable restraint wiring harnesses connect the sensing and diagnostic module (SDM), inflator modules, 
passenger presence system (PPS), electronic frontal sensors (EFS), seat position switches (SPS), passenger seat 
belt tension retractor sensor, and the class 2 serial data circuit together using weather pack connectors. SIR 
deployment loop connectors are yellow in color for easy identification. When repairing SIR system wiring 
harnesses, follow the proper testing and wiring repair procedures outlined in this manual. 

Steering Wheel and Column 

The steering wheel and column are designed to absorb energy when driver contact is made with the steering 
wheel or inflated air bag. In a frontal collision the driver may contact the steering wheel directly or load the 
steering wheel and column through the inflated air bag. When the driver applies load to the air bag or steering 
wheel the column will compress downward absorbing some of the impact, helping to reduce bodily injuries to 
the driver. The steering wheel and column must be inspected for damage after a collision. 

Driver and Passenger Knee Bolsters 

The knee bolsters are designed to help restrain the lower torsos of front seat occupants by absorbing energy 
through the front seat occupants' upper legs. In a frontal collision the front seat occupants legs may come in 
contact with the knee bolsters. The knee bolsters are designed to crush or deform absorbing some of the impact, 
which helps 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 damage after a collision. 

SPECIAL TOOLS AND EQUIPMENT 

SPECIAL TOOLS 

Special Tools 

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Tool Number/Description

 

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J 38715-A 

SIR Driver/Passenger Load Tool

J 38826 

SIR Deployment Harness

J 39401-B 

SIR Deployment Fixture

 

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2004 RESTRAINTS SIR - Hummer H2