start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 46, the reader should be able to: • • • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “H” (Accessories Diagnosis and Repair) List the safety precautions for working around an airbag Describe the procedures to diagnose and troubleshoot airbag faults Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: airbag • arming sensor clockspring deceleration sensor • dual-stage airbags event data recorder (EDR) • event file integral sensor occupant detection systems Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: passenger presence system (PPS) • pretensioners squib • supplemental air restraints (SAR) • supplemental inflatable restraints (SIR) • supplemental restraint system (SRS) unbelted Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SAFETY BELTS AND RETRACTORS Safety Belts Used to keep the driver and passengers secured to the vehicle in the event of a collision Most safety belts include threepoint support and are constructed of nylon webbing The support points include two points on either side of the seat for the belt over the lap and one crossing over the upper torso, which is attached to the “B” pillar or seat back Every crash has three types of collisions: Collision 1—The vehicle strikes another vehicle or object Collision 2—The driver and/or passengers hit objects inside the vehicle if unbelted Collision 3—The internal organs of the body hit other organs or bones, which causes internal injuries Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 If a safety belt is being worn, the belt stretches, absorbing a lot of the impact, thereby preventing collision with other objects in the vehicle and reducing internal injuries Figure 46–1 (a) Safety belts are the primary restraint system (b) During a collision the stretching of the safety belt slows down the impact to help reduce bodily injury Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Belt Retractors Safety belts are also equipped with one of the following types of retractors: Nonlocking retractors, which are usually only used on recoiling lap belts Emergency locking retractors, which lock the position of the safety belt in the event of a collision or rollover Emergency and web speed-sensitive retractors, which allow freedom of movement for the driver and passenger but lock if the vehicle is accelerating too fast or if the vehicle is decelerating too fast Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 See Figure 46–2 for an example of an inertia-type seat belt locking mechanism Safety Belt Lights and Chimes All late-model vehicles are equipped with a safety belt warning light on the dash and a chime that sounds if the belt is not fastened See Figure 46–3 Some vehicles will intermittently flash the reminder light and sound a chime until the driver and sometimes the front passenger fasten their safety belts Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 46–2 Most safety belts have an inertia-type mechanism that locks the belt in the event of rapid movement Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 46–3 A typical safety belt warning light ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PRETENSIONERS A pretensioner is an explosive (pyrotechnic) device that tightens the seat belt as the airbag is being deployed 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 See Figure 46–4 Pretensioners are explosive devices that could be ignited if voltage is applied to the terminals Do not use a jumper wire or powered test light around the wiring near the seat belt latch wiring Always follow the vehicle manufacturer’s recommended test procedures Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OCCUPANT DETECTION SYSTEMS United States Federal Motor Vehicle Safety Standard 208 specifies that the passenger side airbag be disabled or deployed with reduced force under the following conditions This system is referred to as an occupant detection system, also called the passenger presence system (PPS) When there is no weight on the seat and no seatbelt is fastened, the passenger side airbag will not deploy and the airbag disable light should be off The passenger side airbag will be disabled and the disabledairbag light on if only 10 to 37 pounds (4.5 to 17 kg) are on the passenger seat, which would represent a seated child Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 If 38 to 99 pounds (17 to 45 kg) is detected on the passenger seat, which represents a child or small adult, the airbag will deploy at a decreased force If 99 pounds (45 kg) or more is detected on the passenger seat, the airbag will deploy at full force, depending on the severity of the crash, speed of the vehicle, and other factors which may result in the airbag deploying at a reduced force Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The occupant detection systems use one of three types of sensors Gel-filled bladder sensor This sensor uses a silicone-filled bag with a pressure sensor attached The weight of the passenger is measured by the pressure sensor, which sends a voltage signal to the module controlling the airbag deployment The module uses information from both the bladder and the seat belt sensor to determine if a tightened belt may be used to restrain a child seat Figure 46–18 A bladder-type occupant detection sensor showing the pressure sensor and wiring Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Capacitive strip sensors This type of occupant sensor uses several flexible conductive metal strips under the seat cushion These sensor strips transmit and receive a low-level electric field, which changes due to the weight of the front passenger seat occupant The module determines the weight of the occupant Force-sensing resistor sensors This type of occupant sensor uses resistors, which change their resistance based on the stress that is applied These resistors are part of the seat structure, and the module can determine the weight of the occupant based on the change in the resistance of the sensors See Figure 46-19 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 46–19 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 CAUTION: Because resistors are part of the seat structure, it is very important that all seat fasteners be torqued to factory specs to ensure proper operation of the occupant detection system A seat track position sensor is used by the airbag controller to determine the seat position If the seat is too close to the airbag, the controller may disable the airbag Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Diagnosing Occupant Detection Systems A fault in the system may cause the passenger-side airbag light to turn on when there is no weight on the seat A scan tool is often used to check or calibrate the seat, which must be empty, by commanding the module to rezero the seat sensor Some systems, such as on DaimlerChrysler vehicles, use a unit that has various weights along with a scan tool to calibrate and diagnose the occupant detection system Figure 46–20 A test weight is used to calibrate the occupant detection system on a Chrysler vehicle Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SEAT AND SIDE-CURTAIN AIRBAGS Side-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 46–21 A typical seat (side) airbag that deploys from the side of the seat Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Most side-airbag sensors use an electronic accelerometer to detect when to deploy the airbags, which are usually mounted to the bottom of the left and right B-pillars (where the front doors latch) behind a trim panel on the inside of the vehicle Side-curtain airbags are usually deployed by the side-curtain airbag module based on input from many different sensors, including a lateral acceleration sensor and wheel speed sensors CAUTION: Avoid using a lockout tool (for example, a “slim jim”) in vehicles equipped with side airbags to help prevent damage to the components and wiring in the system Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 They are part of the airbag controller on many vehicles The parameters recorded include: Vehicle speed Brake on/off Seat belt fastened G-forces as measured by the accelerometer Unlike an airplane event data recorder, a vehicle unit is not a separate unit and does not record voice conversations or include all crash parameters Additional crash data, such as skid marks and physical evidence at the crash site will still be needed Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The data is constantly being stored in a memory buffer and not recorded into the EPROM unless an airbag deployment has been commanded The data is known as an event file The airbag is commanded based on input from the accelerometer sensor, usually built into the airbag controller, located inside the vehicle The accelerometer calculates the rate of change of the speed of the vehicle The airbags will be deployed if the threshold g-value is exceeded The passenger-side airbag will also be deployed unless it is suppressed because of either of the following: No passenger is detected The passenger-side airbag switch is off Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Data Extraction Data 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 These groups or organizations include: Original equipment manufacturer’s representatives National Highway Traffic Safety Administration Law enforcement agencies Accident reconstruction companies Crash data retrieval must done by a person who has been trained as a crash data retrieval (CDR) technician or analyst, which requires specialized training and the passing of an examination An analyst must attend additional training beyond that of a technician to achieve CDR analyst certification Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Aggressive Driving and OnStar® If a vehicle equipped with the OnStar ®system is being driven aggressively and the electronic stability control system has to intercede to keep the vehicle under control, OnStar ®may call the vehicle to see if there has been an accident The need for a call from OnStar ® usually will be determined if the accelerometer registers slightly over one-g of force, which could be achieved while driving on a race track Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 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 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) All electrical terminals are gold-plated to protect against corrosion Pretensioners are explosive (pyrotechnic) devices that 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458