It’s simple. If you work on any components of the Supplemental Inflatable Restraint (SIR) system without disabling the system, you run the risk of an inadvertent airbag deployment, which is dangerous and costly.
Here’s a possible scenario. A vehicle comes into the dealership with an illuminated airbag MIL and a DTC set in the Sensing and Diagnostic Module (SDM). The technician determines that the SDM should be replaced. But the new SDM fails programming because a DTC is still set. Frustrated by the misdiagnosis, the technician quickly picks up the connected SDM without thinking twice. You know what happens next. The SDM interprets the movement as a rollover event and the system deploys the airbags. This type of scenario can occur with the vehicle off and sitting stationary in the service bay.
The point is to never get too comfortable working around any SIR components and to always follow the proper safety procedures, including disabling the SIR system. Failure to observe the proper procedures while working with the SIR system could cause airbag deployment, personal injury, and unnecessary SIR system repairs.
All Service Information warnings should be followed at all times, including the following warning for the SIR system:
When performing service on or near the SIR components or the SIR wiring, the SIR system must be disabled. Failure to observe the correct procedure could cause deployment of the SIR components. Serious injury can occur. Failure to observe the correct procedure could also result in unnecessary SIR system repairs.
In order to help avoid accidental airbag deployment, anytime a vehicle requires repair of the SIR system and another vehicle system, it’s recommended that repairs be made to the SIR system first, and then repairs made on the other system.
In addition, the ignition should be in the Off position for any service work that requires impact to the body or frame. For example, when adjusting the side door striker using a hammer or mallet.
SIR Component Locations
Components of the SIR system are installed in various locations around a vehicle (Fig. 5). Refer to the SIR Identification Views in the appropriate Service Information to find the location of the SIR components when servicing a vehicle.
Also refer to SIR component and wiring location views in Supplemental Inflatable Restraint before performing a service on or around Supplemental Inflatable Restraint components or wiring.
Disabling the SIR system
Here’s when and how the SIR system should be disabled.
To disable the SIR system by disconnecting the negative battery cable:
- Turn the steering wheel so that the vehicles wheels are pointing straight ahead.
- Place the ignition in the Off position.
- Disconnect the negative battery cable from the battery.
- Wait 2 minutes before working on system.
Handling the SDM
There is a warning label on the SDM. It should never be unbolted or disconnected from the vehicle without first disabling the SIR system. (Fig. 6) The SDM is equipped with a rollover sensor. Turning the SDM over while under power may result in airbag deployment. If the unbolted module it picked up or tilted, and the system is powered, the SDM may see this as a rollover event and the system will respond accordingly. In addition, do not strike or jolt the SDM, which may also be interpreted as a rollover or collision.
The SDM also maintains a reserved energy supply that provides deployment power for the air bags if the module loses battery power during a collision. Deployment power is available for as much as 2 minutes after disconnecting the vehicle power. Wait 2 minutes before working on any SIR system after disabling the system to prevent deployment of the air bags from the reserved energy supply.
Because of the possibility of deployment, the SDM fasteners should not be removed until the battery is disconnected and the SDM electrical connector is removed. The fasteners should be reinstalled and torqued to the proper specifications before reattaching the SDM electrical connector. The electrical connector must be reattached before reconnecting the negative battery cable to the battery.
For additional information, refer to GM training course 22048.55V – Preventing Unintended Airbag Deployment (U.S.) and Bulletin #16-NA-055: Information Regarding Servicing Components Located Near SIR Components.
– Thanks to Len Tillard