Hummer H2. Manual - part 2086

deployment harnesses. 

36. Separate one set of wires and touch the wire ends to the power source in order to deploy the inflator 

modules.  

37. Disconnect the deployment harness from the power source and twist the wire ends together.  

38. Continue the same process with the remaining deployment harnesses that are available.  

39. Remove the drop cloth from the vehicle.  

40. Disconnect all harnesses from the vehicle.  

41. Discard the harnesses.  

42. Scrap the vehicle in the same manner as a non-SIR equipped vehicle.  

43. If one or more of the inflator modules did not deploy, perform the following steps to remove the 

undeployed modules from the vehicle: 

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If the steering wheel module did not deploy, refer to Inflatable Restraint Steering Wheel Module 
Replacement .  

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If the IP module did not deploy, refer to Inflatable Restraint Instrument Panel Module 
Replacement .  

44. Call the Technical Assistance Group for further assistance.  

DESCRIPTION AND OPERATION 

SIR SYSTEM DESCRIPTION AND OPERATION 

SIR System Overview 

The supplemental inflatable restraint (SIR) system supplements the protection offered by the occupant's seat 
belt system (2). The SIR system may contain several inflator modules located throughout the vehicle, i.e. 
steering wheel module (1) and instrument panel (I/P) module (1).Each inflator module has a deployment loop 
that is controlled by the sensing and diagnostic module (SDM) mounted inside the vehicle. The SDM 
determines the severity of a collision with the assistance of various sensor inputs. When the SDM detects a 
collision of sufficient force it will process the information provided by the sensors to further support air bag 
deployment. The SDM performs continuous diagnostic monitoring of the SIR system electrical components. 
Upon detection of a circuit malfunction, the SDM will set a DTC and inform the driver by turning the AIR 
BAG indicator ON. The steering column (1) 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 
passenger. 

IMPORTANT: The inflator module will deploy when the wire ends contact the power 

source.

 

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Fig. 84: Deployed Inflatable Restraint 
Courtesy of GENERAL MOTORS CORP. 

Frontal SIR System Description 

 

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2004 RESTRAINTS SIR - Hummer H2

  

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 

 

2004 Hummer H2 

2004 RESTRAINTS SIR - Hummer H2