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Marc
Marc, Technician
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Experience:  33 years exp. automotive repair NYS emisisions repair cert.
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99 chevy: airbag light..the airbag could malfunction and blow..deploy

Customer Question

i have a 99 chevy lumina.the airbag light is on and i worried the airbag could malfunction and blow up in my face.is there a way to deactivate the airbag so it wont deploy till i get it to be looked at?
Submitted: 11 years ago.
Category: Car
Expert:  Marc replied 11 years ago.

  When that light is on it is deactivated but you can disarm it manuly but is illegal to do so.


Driver's side and passenger air bags are standard equipment on all models covered by this guide. The Supplemental Inflatable Restraint (SIR) system offers protection in addition to that provided by the seat belt by deploying an air bag from the center of the steering wheel or dash panel. The air bag deploys when the vehicle is involved in a frontal crash of sufficient force up to 30° off the centerline of the vehicle. To further absorb the crash energy, there is also a knee bolster located beneath the instrument panel in the driver's area and the steering wheel is collapsible.


Click image to see an enlarged view
Fig. 1: SIR system deployment window



 


The system has an energy reserve, which can store a large enough electrical charge to deploy the air bag(s) for up to ten minutes after the battery has been disconnected or damaged. The system MUST be disabled before any service is performed on or around SIR components or SIR wiring.



 


SYSTEM OPERATION


The SIR system contains a deployment loop for each air bag and a Diagnostic Energy Reserve Module (DERM). The deployment loop supplies current through the inflator module which will cause air bag deployment in the event of a frontal collision of sufficient force. The DERM supplies the necessary power, even if the battery has been damaged.


The deployment loop is made up of the arming sensors, coil assembly, inflator module and the discriminating sensors. The inflator module is only supplied sufficient current when the arming sensor and at least one of the two discriminating sensors close simultaneously. The function of the DERM is to supply the deployment loop a 36 Volt Loop Reserve (36VLR) to assure sufficient voltage to deploy the air bag if ignition voltage is lost in a frontal crash.


The DERM, in conjunction with the sensor resistors, makes it possible to detect circuit and component malfunctions within the deployment loop. If the voltages monitored by the DERM fall outside expected limits, the DERM will indicate a malfunction by storing a diagnostic trouble code and illuminating the AIR BAG lamp.



 


SYSTEM COMPONENTS


See Figure 2



 


Diagnostic Energy Reserve Module (DERM)


The DERM is designed to perform five main functions: energy reserve, malfunction detection, malfunction recording, driver notification and frontal crash recording.


Click image to see an enlarged view
Fig. 2: SIR system components



 


The DERM maintains a reserve voltage supply to provide deployment energy for a few seconds when the vehicle voltage is low or lost in a frontal crash. The DERM performs diagnostic monitoring of the SIR system and records malfunctions in the form of diagnostic trouble codes, which can be obtained from a hand scan tool and/or on-board diagnostics. The DERM warns the driver of SIR system malfunctions by controlling the AIR BAG warning lamp and records SIR system status during a frontal crash.



 


AIR BAG Warning Lamp


The AIR BAG warning/indicator lamp is used to verify lamp and DERM operation by flashing 3 times when the ignition is first turned ON. It is also used to warn the driver of an SIR system malfunction.



 


Discriminating Sensors


All vehicles covered by this guide are equipped with two discriminating sensors. The forward discriminating sensor is located in front of the radiator. The passenger compartment discriminating sensor is located behind the right side of the instrument panel.


The discriminating sensor consists of a sensing element, diagnostic resistor and normally open switch contacts. The sensing element closes the switch contact when vehicle velocity changes are severe enough to warrant air bag deployment.



 


Dual Pole Arming Sensor


The dual pole arming sensor is contained in the same housing as the passenger compartment discriminating sensor and is referred to as the dual sensor.


The arming sensor is a switch located in the power side of the deployment loop. It is calibrated to close at low level velocity changes (lower than the discriminating sensors), assuring that the inflator module is connected directly to the 36VLR output of the DERM or Ignition 1 voltage when any discriminating sensor closes.



 


SIR Coil Assembly


See Figure 3


The SIR coil assembly consists of two current carrying coils. They are attached to the steering column and allow rotation of the steering wheel while maintaining continuous deployment loop contact through the inflator module.


Click image to see an enlarged view
Fig. 3: SIR coil assembly



 


There is a shorting bar on the lower steering column connector that connects the SIR coil to the SIR wiring harness. The shorting bar shorts the circuit when the connector is disengaged. The circuit to the inflator module is shorted in this way to prevent unwanted air bag deployment when servicing the steering column or other SIR components.



 


Inflator Module


The inflator module consists of an inflatable bag and an inflator (a canister of gas-generating material and an initiating device). When the vehicle is in a frontal crash of sufficient force to close the arming sensor and at least one discriminating sensor simultaneously, current flows through the deployment loop. Current passing through the initiator ignites the material in the inflator module, causing a reaction which produces a gas that rapidly inflates the air bag.


All vehicles are equipped with a driver's side inflator module located in the steering wheel and a passenger side inflator module located in the dash panel.



 


SERVICE PRECAUTIONS


See Figures 4 and 5




  • When performing service around the SIR system components or wiring, the SIR system MUST be disabled. Failure to do so could result in possible air bag deployment, personal injury or unneeded SIR system repairs.



  • When carrying a live inflator module, make sure that the bag and trim cover are pointed away from you. Never carry the inflator module by the wires or connector on the underside of the module. In case of accidental deployment, the bag will then deploy with minimal chance of injury.



  • When placing a live inflator module on a bench or other surface, always face the bag and trim cover up, away from the surface.


Click image to see an enlarged view
Fig. 4: When carrying a live inflator module, make sure that the bag and trim cover are pointed away from you. Never carry the inflator module by the wires or connector on the underside of the module



 


Click image to see an enlarged view
Fig. 5: Follow all the manufacturer's cautions when working on an air bag equipped vehicle




 


DISABLING THE SYSTEM


See Figure 6



 


With the AIR BAG fuse removed and the ignition switch


ON, the AIR BAG warning lamp will be on. The is normal and does not indicate any system malfunction.




  1. Turn the steering wheel so that the vehicle's wheels are pointing straight ahead.



  2. Turn the ignition switch to LOCK, remove the key, then disconnect the negative battery cable.



  3. Remove the AIR BAG fuse from the fuse block.



  4. Remove the steering column filler panel.



  5. Disengage the Connector Position Assurance (CPA) and both yellow two way connectors and corresponding CPAs located near the base of the steering column.



  6. Connect the negative battery cable.



 


ENABLING THE SYSTEM


See Figure 6




  1. Disconnect the negative battery cable.



  2. Turn the ignition switch to LOCK, then remove the key.



  3. Engage both yellow SIR connectors and corresponding CPAs located near the base of the steering column.



  4. Install the steering column filler panel.



  5. Install the AIR BAG fuse to the fuse block.



  6. Connect the negative battery cable.



  7. Turn the ignition switch to RUN and make sure that the AIR BAG warning lamp flashes seven times and then shuts off. If the warning lamp does not shut off, make sure that the wiring is properly connected. If the light remains on, take the vehicle to a reputable repair facility for service.


Click image to see an enlarged view
Fig. 6: Location of the driver and passenger side SIR connectors


 
























Customer: replied 11 years ago.
Reply to enginboy's Post: if i remove the fuse does it stop the airbag from deploying at all?
Expert:  Steve replied 11 years ago.
Hello;

   If the airbag light is on, it means that the system is not operational and is extremely unlikely to deploy. Whenever you start the car, the airbag system runs a self test, and if any of teh components or circuits in the system do not respond properly the airbag controller shuts the system down so as to not deploy, even in a collision.
   Disarming the system manually isn't very easy; most of tehm have a direct power feed from battery voltage somewhere which must be disabled.   
   I would not be afraid to drive the vehicle untill you get it repaired; I t is very unlikely to accidentally go off since the engineers design them to shut down unless they are in perfect working order.    You should be aware however, that if teh light is ON the system will not work at all, even in a crash.
Expert:  Marc replied 11 years ago.

  If you remove the fuse and disconnect the connector mentioned in Fig 6 the air bag are in servicable safe mode  NOTE this is not recommended for driving.


   Your air bag is not going to deploy because the light is on in fact if you have an accident while the light is on it more then likely WILL NOT DEPLOY.

   As I stated previously You cut the backup power witch completely disables the system by disconecting the plug in Fig 6 This is easy to do not like Mr Rap states.[Quote]  Disarming the system manually isn't very easy; most of tehm have a direct power feed from battery voltage somewhere which must be disabled.[/Quote] Every thing is explained in my first post.

 
Expert:  Marc replied 11 years ago.

 

You should also chech fuse number 21


   Has the passeger side floor ever gotten wet because the sensing -dianostic module is located under the front seat on passenger side. If it gat wet that could be where your problem ios coming from. If so report this when you bring the car in for service.

Marc, Technician
Category: Car
Satisfied Customers: 1888
Experience: 33 years exp. automotive repair NYS emisisions repair cert.
Marc and 2 other Car Specialists are ready to help you
Customer: replied 11 years ago.
Reply to enginboy's Post: thank you for putting my mind at ease!:)
Expert:  Steve replied 11 years ago.
   I must disagree slightly with engineboy's reply above; while he is correct that the system can be disabled as he describes, it isn't quite as easy as it sounds if you are not as familiar with vehicle repair as we are.
   To one of us, removing the arming connector under the dash (see figure 6) isn't much of a challenge, but it does involve removing some trim panels from under the dash and locating the proper connector among a jungle of otehr electrical connectors and wiring, and disconnecting it without damaging it (which would result in having to replace the $150 clockspring assembly to make teh system functional again).   The other option would be as I mentioned in my original post, locating and disconnecting battery feed to the SIR controller.
   In any case, even if you don't disconnect anything, the airbag will not go off unless there is some sort of b+ short in teh steering column wiring that would supply power to the inflator module accidentally; and if this is the case disconnecting any or all of the aforementioned components would have no result.
   Respectfully,
Steve Rapp, 23 yr Master technician,
GM trained in SIR system repair

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