OBJECTIVES After studying Chapter 26, the reader should be able to: Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “H” (Accessories Diagnosis an Repair). List the safety precautions for working around an airbag. Describe the procedures to diagnose and troubleshoot airbag faults.

AIRBAGS Airbags may be known by many different names including the following: 1. Supplemental restraint system (SRS) 2. Supplemental inflatable restraints (SIR) 3. Supplemental air restraints (SAR)

AIRBAGS Operation The parts include: 1. Sensors 2. Airbag (inflator) module 3. Clockspring wire coil in the steering column 4. Control module 5. Wiring and connectors

AIRBAGS Operation FIGURE 26-1 A typical airbag system showing many of the components.

AIRBAGS Operation To cause inflation, the closing of the arming sensor is required to provide the power-side voltage to the inflator module. In other words, two sensors must be triggered at the same time before the airbag will be deployed. FIGURE 26-2 A simplified airbag deployment circuit. Note that both the arming sensor and at least one of the discriminating sensors must be activated at the same time. The arming sensor provides the power and either one of the discriminating sensors can provide the ground for the circuit.

AIRBAGS Types of Airbag Inflators There are two different types of inflators used in airbags, including: 1. Solid fuel. This type uses sodium azide pellets and, when ignited, generates a large quantity of nitrogen gas that quickly inflates the airbag. FIGURE 26-3 Lifting the squib from the airbag housing. The squib is the heating element that ignites the pyrotechnic gas generator that rapidly produces nitrogen gas to fill the airbag.

AIRBAGS Types of Airbag Inflators 2. Compressed gas. Commonly used in passenger side airbags and roof-mounted systems, this system uses a canister filled with argon gas, plus a small percentage of helium at 3,000 psi (435 kPa). FIGURE 26-4 A deployed side-curtain airbag on a training vehicle.

AIRBAGS Sensors There are three basic styles (designs) of airbag sensors. 1. Magnetically retained gold-plated ball sensor. This sensor uses a permanent magnet to hold a gold-plated steel ball away from two gold-plated electrical contacts. FIGURE 26-5 An airbag magnetic sensor.

AIRBAGS Sensors 2. Rolled up stainless-steel ribbon-type sensor. This sensor is housed in an airtight package with nitrogen gas inside to prevent harmful corrosion of the sensor parts. FIGURE 26-6 Some vehicles use a ribbon-type crash sensor.

AIRBAGS Sensors 3. Integral sensor. Some vehicles use electronic deceleration sensors built into the inflator module. FIGURE 26-7 Notice that within 1/4 second of a collision, the sensors have closed, the airbag has deployed, and the airbag has deflated.

AIRBAGS Wiring To ensure proper electrical connection to the inflator module in the steering wheel, a coil assembly is used in the steering column. This coil, usually called a clockspring, prevents the lack of continuity between the sensors and the inflator assembly that might result from a horn-ring type of sliding conductor.

AIRBAGS Wiring FIGURE 26-8 The airbag control module is linked to the powertrain control module (PCM) and the body control module (BCM) on this Chrysler system. Notice the airbag wire connecting the module to the airbag through the clockspring.

AIRBAGS Wiring Most airbag systems also contain a diagnostic unit that often includes an auxiliary power supply, which is used to provide the current to inflate the airbag if the battery is disconnected from the vehicle during a collision. This auxiliary power supply normally uses capacitors that are discharged through the squib of the inflation module.

AIRBAGS Wiring FIGURE 26-10 An airbag diagnostic tester. Included in the plastic box are electrical connectors and a load tool that substitutes for the inflator module during troubleshooting. FIGURE 26-9 An airbag being deployed as part of a demonstration in an automotive laboratory.

AIRBAGS Troubleshooting The electrical portion of most airbag systems is constantly checked by the circuits within the airbag-energizing power unit or through the vehicle’s computer system. Follow exact manufacturer’s recommended procedures for accessing and erasing airbag diagnostic trouble codes.

AIRBAG DIAGNOSIS TOOLS AND EQUIPMENT Diagnosis and service of airbag systems usually require some or all of the following items. Digital multimeter (DMM) Airbag simulator, often called a load tool Scan tool Shorting bar or shorting connector(s) Airbag system tester Vehicle-specific test harness Special wire repair tools or connectors, such as crimp-and seal weatherproof connectors

AIRBAG DIAGNOSIS TOOLS AND EQUIPMENT Precautions Take the following precautions when working with or around airbags. 1. Always follow all precautions and warning stickers on vehicles equipped with airbags. 2. Maintain a safe working distance from all airbags to help prevent the possibility of personal injury in the unlikely event of an unintentional airbag deployment. 3. In the event of a collision in which the bag(s) is deployed, the inflator module and all sensors usually must be replaced to ensure proper future operation of the system.

AIRBAG DIAGNOSIS TOOLS AND EQUIPMENT Precautions 4. Avoid using a self-powered test light around the yellow airbag wiring. Even though it is highly unlikely, a self powered test light could provide the necessary current to accidentally set off the inflator module and cause an airbag deployment. 5. Use care when handling the inflator module section when it is removed from the steering wheel. Always hold the inflator away from your body. 6. If handling a deployed inflator module, always wear gloves and safety glasses to avoid the possibility of skin irritation from the sodium hydroxide dust, which is used as a lubricant on the bag(s), that remains after deployment.

AIRBAG DIAGNOSIS TOOLS AND EQUIPMENT Precautions 7. Never jar or strike a sensor. The contacts inside the sensor may be damaged, preventing the proper operation of the airbag system in the event of a collision. 8. When mounting a sensor in a vehicle, make certain that the arrow on the sensor is pointing toward the front of the vehicle. Also be certain that the sensor is securely mounted.

AIRBAG TESTING AND SERVICE Airbag system components and their location in the vehicle vary according to system design, but the basic principles of testing are the same as for other electrical circuits. Use service information to determine how the circuit is designed and the correct sequence of tests to be followed.

DRIVER SIDE AIRBAG MODULE REPLACEMENT The following procedure reviews the basic steps for removing an airbag module. 1. Turn the steering wheel until the front wheels are positioned straight ahead. Some components on the steering column are removed only when the front wheels are straight. 2. Switch the ignition off and disconnect the negative battery cable, which cuts power to the airbag module. 3. Once the battery is disconnected, wait as long as recommended by the manufacturer before continuing. When in doubt, wait at least 10 minutes to make sure the capacitor is completely discharged.

DRIVER SIDE AIRBAG MODULE REPLACEMENT 4. Loosen and remove the nuts or screws that hold the airbag module in place. On some vehicles, these fasteners are located on the back of the steering wheel. On other vehicles, they are located on each side of the steering wheel. The fasteners may be concealed with plastic finishing covers that must be pried off with a small screwdriver to access them.

DRIVER SIDE AIRBAG MODULE REPLACEMENT 5. Carefully lift the airbag module from the steering wheel and disconnect the electrical connector. Connector location varies: Some are below the steering wheel behind a plastic trim cover; others are at the top of the column under the module. 6. Store the module pad side up in a safe place where it will not be disturbed or damaged while the vehicle is being serviced. Do not attempt to disassemble the airbag module. If the airbag is defective, replace the entire assembly.

DRIVER SIDE AIRBAG MODULE REPLACEMENT FIGURE 26-12 Shorting bars are used in most airbag connectors. These spring-loaded clips short across both terminals of an airbag connector to help prevent accidental deployment of the airbag. If electrical power was applied to the terminals the shorting bars would simply provide a low-resistance path to the other terminal and not allow current to flow past the connector. The mating part of the connector has a tapered piece that spreads apart the shorting bars. FIGURE 26-11 The process of removing the airbag inflator module from the steering wheel and disconnecting the yellow airbag electrical connector.

DRIVER SIDE AIRBAG MODULE REPLACEMENT When installing the airbag module, make sure the clockspring is correctly positioned to ensure module-to-steering column continuity. FIGURE 26-13 A typical coil assembly (often called a clockspring) is used to electrically connect the inflation module with the airbag module that actually supplies the voltage at the time of a collision to deploy the airbag. It is critical that the column-mounted coil assembly be installed correctly.

SAFETY WHEN MANUALLY DEPLOYING AIRBAGS Do the following to prevent injury when manually deploying an airbag. When possible, deploy the airbag outside of the vehicle. Follow the vehicle manufacturer’s recommendations. When deploying the airbag inside the vehicle, make sure personnel, tools, and equipment are removed from inside the vehicle. Wear the proper hearing and eye protection. Deploy the airbag with the trim cover facing up. Stay at least 20 ft (6 ms) from the airbag. Allow the airbag module to cool.

PRETENSIONERS The purpose of the pretensioning device is to force the occupant back into position against the seat back and to remove any slack in the seat belt. FIGURE 26-14 A small explosive charge forces the end of the seat belt down the tube, which removes any slack in the seat belt.

OCCUPANT DETECTION SYSTEMS This system is referred to as an occupant detection system, or the passenger presence system (PPS). The PPS use one of three types of sensors. Gel-filled bladder sensor. Capacitive strip sensors. Force-sensing resistor sensors.

OCCUPANT DETECTION SYSTEMS FIGURE 26-16 A resistor-type occupant detection sensor. The weight of the passenger strains these resistors, which are attached to the seat, thereby signaling to the module the weight of the occupant. FIGURE 26-15 A bladder-type occupant detection sensor showing the pressure sensor and wiring.

OCCUPANT DETECTION SYSTEMS Diagnosing Occupant Detection Systems Some systems, such as those used on Chrysler vehicles, use a unit that has various weights along with a scan tool to calibrate and diagnose the occupant detection system. FIGURE 26-17 A test weight is used to calibrate the occupant detection system on a Chrysler vehicle.

SEAT AND SIDE CURTAIN AIRBAGS Side and/or curtain airbags use a variety of sensors to determine if they need to be deployed. Side airbags are mounted in one of two general locations. In the side bolster of the seat In the door panel FIGURE 26-18 A typical seat (side) airbag that deploys from the side of the seat.

EVENT DATA RECORDERS Parts and Operation The purpose of the event data recorder (EDR) is to record parameters just before and slightly after an airbag deployment. The parameters recorded include: Vehicle speed Brake on/off Seat belt fastened G-forces as measured by the accelerometer

EVENT DATA RECORDERS Parts and Operation The passenger side airbag will also be deployed unless it is suppressed by either of the following: No passenger is detected. The passenger side airbag switch is off.

EVENT DATA RECORDERS Data Extraction Data extraction from the event data recorder in the airbag controller can only be achieved using a piece of equipment known as the Crash Data Retrieval System, manufactured by Vetronics Corporation. This is the only authorized method for retrieving event files and only certain organizations are allowed access to the data.

TEMPORARY DISCONNECTION OF AIRBAGS Step-by-Step

TEMPORARY DISCONNECTION OF AIRBAGS Step-by-Step cont

TEMPORARY DISCONNECTION OF AIRBAGS Step-by-Step cont

TEMPORARY DISCONNECTION OF AIRBAGS Step-by-Step cont

TEMPORARY DISCONNECTION OF AIRBAGS Step-by-Step cont

TEMPORARY DISCONNECTION OF AIRBAGS Step-by-Step cont

SUMMARY Airbags use a sensor(s) to determine if the rate of deceleration is enough to cause bodily harm. All airbag wiring is yellow. When working around an airbag, disconnect the wiring connectors to help prevent accidental deployment. Frontal airbags only operate within 30 degrees from center and do not deploy in the event of a rollover, side, or rear collision. Two sensors must be triggered at the same time for an airbag deployment to occur.

SUMMARY All electrical terminals are gold plated to protect against corrosion. Pretensioners are explosive (pyrotechnic) devices which remove the slack from the seat belt and help position the occupant. Occupant detection systems use sensors in the seat to determine whether the airbag will be deployed and with full or reduced force.

REVIEW QUESTIONS What are the safety precautions to follow when working around an airbag? What sensor(s) must be triggered for an airbag deployment? How should deployed inflation modules be handled? What is the purpose of pretensioners?

CHAPTER QUIZ A vehicle is being repaired after an airbag deployment. Technician A says that the inflator module should be handled as if it is still live. Technician B says rubber gloves should be worn to prevent skin irritation. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ A vehicle is being repaired after an airbag deployment. Technician A says that the inflator module should be handled as if it is still live. Technician B says rubber gloves should be worn to prevent skin irritation. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

2. A seat belt pretensioner is _________. CHAPTER QUIZ 2. A seat belt pretensioner is _________. A device that contains an explosive charge Used to remove slack from the seat belt in the event of a collision Used to force the occupant back into position against the seat back in the event of a collision All of the above

2. A seat belt pretensioner is _________. CHAPTER QUIZ 2. A seat belt pretensioner is _________. A device that contains an explosive charge Used to remove slack from the seat belt in the event of a collision Used to force the occupant back into position against the seat back in the event of a collision All of the above

3. What conducts power and ground to the driver’s side airbag? CHAPTER QUIZ 3. What conducts power and ground to the driver’s side airbag? Twisted-pair wires Clockspring Carbon contact and brass surface plate on the steering column Magnetic reed switch

3. What conducts power and ground to the driver’s side airbag? CHAPTER QUIZ 3. What conducts power and ground to the driver’s side airbag? Twisted-pair wires Clockspring Carbon contact and brass surface plate on the steering column Magnetic reed switch

CHAPTER QUIZ 4. Two technicians are discussing dual-stage airbags. Technician A says that a deployed airbag is safe to handle regardless of which stage caused the deployment of the airbag. Technician B says that both stages ignite, but at different speeds depending on the speed of the vehicle. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 4. Two technicians are discussing dual-stage airbags. Technician A says that a deployed airbag is safe to handle regardless of which stage caused the deployment of the airbag. Technician B says that both stages ignite, but at different speeds depending on the speed of the vehicle. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

5. Where are shorting bars used? CHAPTER QUIZ 5. Where are shorting bars used? In pretensioners At the connectors for airbags In the crash sensors In the airbag controller

5. Where are shorting bars used? CHAPTER QUIZ 5. Where are shorting bars used? In pretensioners At the connectors for airbags In the crash sensors In the airbag controller

CHAPTER QUIZ 6. Technician A says that a deployed airbag can be repacked, reused, and reinstalled in the vehicle. Technician B says that a deployed airbag should be discarded and replaced with an entire new assembly. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 6. Technician A says that a deployed airbag can be repacked, reused, and reinstalled in the vehicle. Technician B says that a deployed airbag should be discarded and replaced with an entire new assembly. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

7. What color is airbag wiring? CHAPTER QUIZ 7. What color is airbag wiring? Blue Red Yellow Orange

7. What color is airbag wiring? CHAPTER QUIZ 7. What color is airbag wiring? Blue Red Yellow Orange

CHAPTER QUIZ 8. Driver- and/or passenger-side airbags will only deploy if a collision occurs how many degrees from straight ahead? 10 degrees 30 degrees 60 degrees 90 degrees

CHAPTER QUIZ 8. Driver- and/or passenger-side airbags will only deploy if a collision occurs how many degrees from straight ahead? 10 degrees 30 degrees 60 degrees 90 degrees

CHAPTER QUIZ 9. How many sensors must be triggered at the same time to cause an airbag deployment? One Two Three Four

CHAPTER QUIZ 9. How many sensors must be triggered at the same time to cause an airbag deployment? One Two Three Four

CHAPTER QUIZ 10.The electrical terminals used for airbag systems are unique because they are _________. Solid copper Tin-plated heavy-gauge steel Silver plated Gold plated

CHAPTER QUIZ 10.The electrical terminals used for airbag systems are unique because they are _________. Solid copper Tin-plated heavy-gauge steel Silver plated Gold plated

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