Chapter 27 Restraint System Repairs Objectives Explain the

Chapter 27 Restraint System Repairs

Objectives • Explain the difference between an active and a passive restraint system • Learn how to service seat belts • Describe the operation of air bag systems • Repair are bag systems safely

Introduction • A restraint system is designed to help hold passengers in their seats • Restraint systems prevent passengers from being injured during a collision • All new vehicles come equipped with some form of restraint system

Active and Passive Restraints • An active restraint system is one that the occupants must make an effort to use • Conventional, manually operated seat belts are classified as an active restraint system • A passive restraint system is one that operates automatically • Two types of passive restraint systems are automatic seat belts and air bags

Seat Belt Systems • Seat belts are strong nylon straps with special ends attached for securing people in their seats • Lap belts extend across the lap and shoulder straps extend over the chest and shoulder • Seat belt anchors allow one end of the belts to be bolted to the body structure • A seat belt retractor is used to remove slack from the belts so they fit snugly • Seat belt reminder systems use a warning system to remind the driver to fasten the seat belt

Figure 27 -2. Restraint systems include seat belts and air bags, normally under computer control. Note the location of major parts.

Figure 27 -3. Study the major parts of the seat belt system. Buckles, latches, and belts themselves must be in good condition before release to the customer.

Seat Belt Service • Do not intermix types of seat belts on front or rear seats • Avoid bending or damaging any portion of the belt buckle or latch plate • Always replace lap and shoulder belt retractor mechanisms or lap belt retractor covers • A visual and functional inspection is important – Check for twisted or damaged webbing – Replace the assembly if the buckle will not latch, or if it does not lock when the brake is applied

Child Restraint Systems and Air Bag Safety • Child restraint system is a removable appliance available from most automobile dealers • Restraint seats are available in either rearwardfacing or forward-facing models • The seat is intended to be tightly secured with the vehicle's shoulder or lap belt • The seat should never be used without the special security clip • May late model vehicles are equipped with integral seats built into the rear seat

Air Bag Systems • An air bag system automatically deploys a large nylon bad during severe collisions • Driver's-side air bad is mounted inside the steering wheel center pad • Passenger-side air bag is mounted behind a small door in the side of the instrument panel • Side impact air bags deploy from the door panels or from the side of the front seats • Rear seat air bags fit into the rear cushion of the front seats

Air Bag Systems (continued) • All air bag systems have similar parts: – Air bag module – inflator mechanism and nylon bag that expand – Air bad system sensors – inertia sensors that signal the computer of a collision – Control unit – computer that operates the system – Wiring harness – wiring and connectors that link the system parts – Dash indicator lamp – dash bulb that warns of system problem

Figure 27 -7. Study the major parts of an air bag system.

Air Bag Module • Air bag module is composed of the nylon bag and an igniter-inflator mechanism • Air bag is a strong nylon bag attached to the metal frame of the module • Air bag igniter produces a small spark when an electrical signal is sent from the control unit • Propellant charge is sodium azide, which converts to nitrogen gas as it burns • Knee bolster cushions the driver's knees and prevents the driver from sliding under the air bag

Figure 27 -8. The driver air bag module mounts in the steering wheel. Note part names and locations.

Air Bag Sensors • Impact sensors are the first sensors to detect a collision • Arming sensor ensures that the particular collision is severe enough to require air bags • Inertia sensors detect a rapid deceleration to produce an electrical signal • Seat cushion sensors detect the weight of a person sitting in the passenger seat • Controller analyzes input from the sensors to determine if the bag deployment is needed

The inertia sensor detects rapid deceleration from hard impact on the front or side of the vehicle. It sends a signal to the computer to deploy the air bag. Inertia sensors must be installed with the arrow in the right direction. Also, make sure the system is disarmed so that the new air bag does not deploy while working.

Air Bag System Servicing • Before servicing a vehicle equipped with an air bag, the system must be disarmed • Always disconnect the negative battery cable • Even with the battery disconnected, an energy reserve module can deploy the air bag • After air bag deployment, use a shop vacuum to clean the passenger compartment • Residual powder (eye/skin irritant) can be present

Figure 27 -10. After air bag deployment, the passenger compartment should be vacuumed clean. Wear eye protection and a respirator before removing deployed air bags. Passenger air bag deployment often breaks the windshield. Side air bag deployment can damage the inner trim panel.

Air Bag System Servicing (continued) • Air bag system parts replacement after a deployment will vary • To remove the deployed air bag, remove the small screws from the rear of the steering wheel – Wear safety glasses and a respirator • Inspect all parts for damage and any parts with visible damage should be replaced • When carrying a live air bag module, point the bag and trim cover away from your body

Figure 27 -11. When installing new air bag parts, always follow the service manual instructions. Here a technician is installing a new side air bag on the door. Stay to one side and keep your head away from the bag during installation to avoid injury.

Air Bag System Servicing (continued) • Air bag system performs a self-check every time the ignition is turned to the on position – When complete, the lamp should go off • Make sure a final sweep is made for codes or collision information using the approved scan tool • Recheck the wire and harness routing before releasing the car • Check to make sure the sensors are firmly fastened to the mounting fixtures and all fuses are correctly rated and replaced

Summary • Active restraint system is one that the occupants must make an effort to use • Passive restraint system operates automatically, such as automatic seat belts and air bags • Child seat may be rear facing, front facing, or a combination • Most air bag systems have an air bag module, air bag system sensors, control unit, wiring harness, and dash indicator lamp