Supplemental Inflatable Restraint System: Overview GMC Acadia I

SIR Identification Views

The SIR Identification Views shown below illustrate the approximate location of all SIR components available for the vehicle. This will assist in determining the appropriate SIR Disabling and Enabling for a given service procedure. Refer to SIR Disabling and Enabling .

Scheme 4

Circuit/System Description

During a frontal crash of sufficient force the inflatable restraint sensing and diagnostic module (SDM) will allow current to flow through the deployment loop in order to deploy the steering wheel module. The SDM performs continuous diagnostic tests on the deployment loops to check for proper circuit continuity and for shorts to ground or voltage.

There are 2 shorting bars used within the steering wheel module coil connector which will short together both steering wheel module stage 1 high circuit and steering wheel module stage 1 low circuit and both steering wheel module stage 2 high circuit and steering wheel module stage 2 low circuit when the connector is disconnected. This will help to prevent unwanted deployment of the inflator module during servicing.

During a side or frontal crash of sufficient force the inflatable restraint sensing and diagnostic module (SDM) will allow current to flow through the deployment loop in order to deploy an inflatable restraint module. There are 2 shorting bars used within the module connector which will short together both high and low circuits, when the connector is disconnected. This will help to prevent unwanted deployment of the inflator module during servicing.

The inflatable restraint sensing and diagnostic module (SDM) contains a sensing device that converts vehicle velocity changes into an electrical signal. The SDM compares this electrical signal to a value stored in memory. When the generated signal exceeds the stored value, the SDM performs additional signal processing and compares the generated signals to values stored in memory. When 2 of the generated signals exceed the stored values, the SDM will cause current to flow through the deployment loops

1. Deploying the air bags and/or pretensioners causing DTC B0052 to set.
2. Deploying the side airbags causing DTC B0055 to set with no faults present.

When the ignition is turned ON, the passenger presence system (PPS) and the inflatable restraint sensing and diagnostic module (SDM) performs tests to diagnose critical malfunctions within itself. The PPS is used to monitor the weight of an occupant in the front passenger seat. If the pressure from the occupant's weight is less than a specified value or an empty seat is detected, the PPS module will send a suppress signal to the SDM to disable the instrument panel (I/P) module. When the PPS detects a fault within itself, then the PPS will communicate to the SDM through serial data communications that a PPS fault is present. The SDM will suppress the deployment of the module and then illuminate the AIR BAG indicator.

DTC B0056 sets because the PPS commanded to suppress the I/P inflator module when the vehicle was involved in a collision and the SDM has commanded an air bag deployment.

DTC B0057 sets because the PPS commanded to suppress the side impact module when the vehicle was involved in a collision and the SDM has commanded an air bag deployment.

DTC B0058 sets because the PPS commanded to suppress the seat belt pretensioner when the vehicle was involved in a collision and the SDM has commanded an air bag deployment.

The inflatable restraint seat belt buckle switch is within the seat belt buckle and provides an input to the inflatable restraint sensing and diagnostic module (SDM). The SDM supplies a low reference circuit and a seat belt switch signal circuit to determine a buckled or unbuckled condition. The SDM monitors the seat belt switch circuits, and if a fault is detected a DTC will be set.

The passenger presence system (PPS) sensor continually monitors itself and if a fault in this circuit occurs, a DTC will set. When the sensing and diagnostic module (SDM) detects this DTC within the PPS, it will notify the customer of the enable/disable status by illuminating the OFF indicator on the PASSENGER AIR BAG ON/OFF indicators. Then the PPS will communicate to the SDM through serial data communications that a PPS fault is present. The SDM will then disable the deployment of the instrument panel module and then illuminate the AIR BAG warning indicator.

When the ignition is turned ON, the passenger presence system (PPS) and the inflatable restraint sensing and diagnostic module (SDM) performs tests to diagnose critical malfunctions within itself. When the SDM has completed the power-up mode, the SDM will establish communication with the PPS. The SDM will also request the instrument panel cluster to illuminate both of the PASSENGER AIR BAG ON/OFF indicators. If the SDM detects that the PPS has set a current DTC, the SDM will then disable the instrument panel (I/P) module deployment loop, set DTC B0081, and illuminate the AIR BAG indicator.

The inflatable restraint front end sensor utilizes a bidirectional 2-wire circuit. The front end sensor modulates current on the interface to send ID, state of health, and deployment commands to the inflatable restraint sensing and diagnostic module (SDM). The SDM serves as a power source and a ground for the front end sensor. When the ignition is turned ON and input power from the SDM is first detected, the front end sensor responds by performing internal diagnostics and sending an ID to the SDM. The SDM considers the ID to be valid if the response time is less than 5 seconds. The front end sensor continually communicates status messages to the SDM, which determines if a fault is present in the front end sensor circuit. When a fault is detected, the SDM may reset the front end sensor up to 2 times by removing and reapplying power to it. If the fault is still present, the SDM will set a DTC.

The inflatable restraint sensing and diagnostic module (SDM) stores a 4-digit primary key for the inflatable restraint passenger presence system (PPS). The SDM sends the PPS the primary key. If the PPS determines that it is the wrong primary key, the PPS will set DTC B1001 and send the SDM a vehicle mismatch message. The SDM then will set DTC B0081 and illuminate the SIR warning indicator. The PPS does not use a secondary key.

The inflatable restraint sensing and diagnostic module (SDM) stores a primary data key, which is a 4-digit number, and a secondary data key, which is a portion of the vehicle identification number (VIN). When the ignition is turned ON, the SDM compares this information to the information stored in the body control module (BCM) over the serial data communication circuit.

The vehicle rollover sensor (ROS) monitors the vehicle speed signal (VSS) on the GMLAN serial data circuit. If the VSS is marked as invalid or is missing, the ROS will set a diagnostic trouble code (DTC).

The passenger air bag ON/OFF indicators are used to notify the driver when the Passenger Presence System (PPS) has enabled or disabled the I/P inflator module. When the ignition is turned ON, the ignition voltage is supplied to the passenger air bag ON/OFF indicators and to the PPS module. The instrument panel cluster (IPC) grounds all indicator control circuits to the passenger air bag ON/OFF indicators for illumination. The IPC receives serial data messages from the supplemental inflatable restraints system to turn ON the indicators as necessary.

After the SDM is programmed, the SDM setup procedure is required. During this set up procedure, the SDM will compare the content that was just programmed to the actual components that are installed on the vehicle. If the SDM detects that there are too few or too many components on the system, DTC B1019 00 will set and not allow the setup procedure to complete.

The inflatable restraint sensing and diagnostic module (SDM) monitors the ignition signal from the ignition switch. When the vehicle ignition switch is placed in the RUN or CRANK position, the switch supplies voltage to the SDM ignition input terminal. If an open or short to ground in this SDM ignition circuit is detected, then DTC B1370 will set.

When the ignition is turned ON, the instrument panel cluster (IPC) flashes the air bag indicator 7 times for a bulb check. The inflatable restraint sensing and diagnostic module (SDM) performs diagnostic tests on the SIR system during the bulb check. If any malfunction exists the SDM will request the IPC to illuminate the air bag indicator steady, via serial data. If a preexisting malfunction exists, the air bag indicator will illuminate steady immediately after the ignition is turned ON. If the ignition 1 voltage is outside of the normal operating voltage range 9-16 volts, the SDM will command the IPC to turn the air bag indicator ON with no DTCs present, then disables all deployment loops.

The PASSENGER AIR BAG ON/OFF indicators are used to notify the driver when the Passenger Presence System (PPS) has enabled or disabled the I/P inflator module. When the ignition is turned ON, the PPS illuminates the PASSENGER AIR BAG ON/OFF indicators for 5 seconds. The PPS module conducts tests on the PPS components and circuits while the PASSENGER AIR BAG ON/OFF indicators are illuminated. If no malfunctions are detected, the PPS module will illuminate the PASSENGER AIR BAG indicator ON or OFF, depending on the status of the PPS. If a malfunction is detected, the PPS module will store a diagnostic trouble code (DTC), default the PPS to the OFF state, and communicate with the SDM that a DTC has been set. The SDM will request the IPC to illuminate the AIR BAG indicator to notify the driver of a PPS malfunction.

Frontal SIR System Description

The frontal supplemental inflatable restraint (SIR) system consists of the following components

1. AIR BAG indicator located in the instrument panel cluster (IPC)
2. Inflatable restraint sensing and diagnostic module (SDM)
3. Inflatable restraint passenger presence system (PPS)
4. Inflatable restraint Passenger AIR BAG ON/OFF indicator
5. Inflatable restraint instrument panel (I/P) module
6. Inflatable restraint steering wheel module
7. Inflatable restraint steering wheel module coil
8. Inflatable restraint seat belt retractor pretensioners
9. Inflatable restraint wiring harnesses
10. Steering wheel and column
11. Driver and front passenger knee bolsters

A frontal collision of sufficient force will deploy the frontal air bags and/or pretensioners. The sensing and diagnostic module (SDM) contains a sensing device that converts vehicle velocity changes to an electrical signal. The SDM compares these signals to values stored in memory. If the signals exceed a stored value, the SDM will determine the severity of the impact and either cause current to flow through the frontal deployment loops deploying the frontal air bags and pretensioners, or it will deploy the pretensioners only. The SDM, I/P module, steering wheel module, steering wheel module coil, seat belt retractor pretensioners, and the connecting wires make up the frontal deployment loops. The SDM continuously monitors the deployment loops for malfunctions and illuminates the AIR BAG indicator if a fault is detected.

Side SIR System Description

The side supplemental inflatable restraint (SIR) system consists of the following components

1. AIR BAG indicator located in the instrument panel cluster (IPC)
2. Inflatable restraint sensing and diagnostic module (SDM)
3. Inflatable restraint side impact sensors (SIS)
4. Inflatable restraint roof rail modules
5. Inflatable restraint wiring harnesses