Advanced Automotive Fault Diagnosis
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LÔØI NOÙI ÑAÀU, ledklok
| 9.17.3 Seat belt tensioners
Taking the ‘slack’ out of a seat belt in the event of an impact is a good contribution to vehicle passen- ger safety. The decision to take this action is the same as for the air bag. The two main types are: ● spring tension; ● pyrotechnic. The mechanism used by one type of seat belt tensioner works by explosives. When the explo- sive charge is fired, the cable pulls a lever on the seat belt reel, which in turn tightens the belt. The unit must be replaced once deployed. This fea- ture is sometimes described as anti-submarining. Figure 9.65 shows a full seat belt, air bag system and other safety features. Electrical systems 243 Figure 9.64 Air bag block diagram showing the ‘safing circuit’ Figure 9.65 Seat belts and tensioners (Source: Volvo Media) 9.18 Diagnostics – air bags and belt tensioners 9.18.1 Systematic testing Warning Careless or incorrect diagnostic work could deploy the air bag causing serious injury. Leave well alone if in any doubt. The only reported fault for air bags should be that the warning light is staying on! If an air bag has been deployed then all the major components should be replaced. Some basic tests that can be carried out are as follows. 244 Advanced automotive fault diagnosis Check battery – must be 70% charged Start Air bags and belt tensioners diagnostic chart End Scan for DTCs if equipment is available Disconnect the supplementary restraint system (SRS) fuse or the battery earth lead – to prevent risk of accidental deployment Wait for at least 10 minutes to allow the igniter capacitors to discharge Hand and eye checks (loose wires, loose switches and other obvious faults) – all connections clean and tight Scanner available and shows possible faults? Check circuit where fault is shown Yes No Replace faulty component Reset SRS warning light Pay particular attention to slip ring connections on the steering wheel if appropriate Do not carry out any ohmmeter tests on the air bag circuit tải về 7.07 Mb. Chia sẻ với bạn bè của bạn:
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