What is the requirement for airbags in the MOT? Should they be working? Does the airbag light have to follow a predefined procedure, like the ABS one does?
I've heard a few people say they must be working, and some say that their car has had the light on for 2 MOT's and not failed yet.
the same way the ABS is sort of "tested" with the function light, use the airbag warning function light, ive have seen a few where the airbag light is illuminated when it should'nt be & advised on it, there is a tickbox on the mot computer just for this, if the vehicle was involved in a crash, the airbag failed to inflate & it was noted during a test, it might have implications regards to an insurance claim.
The airbag sensor is a chip with an integrated accelerometer. This is a tiny etched silicon beam with a weight on the end. When an accelerating force is applied the beam bends, which causes a capacitance change that can be measured. An electric field can also be applied to the beam to electrically bend it. The self-test applies an electric field which bends the beam and looks for an appropriate capacitance change - if it doesn't see one within limits then it decides the sensor is faulty.
Cars typically do this check when the ignition is turned, so you'd know quite soon if it thinks there is a problem. There are some things that are more difficult to test (like will the gas fire when asked) but at least it knows the sensor is working without having to have a crash.
The only problem with this is that on most systems it is possible for the light to be on when the system is working perfectly. On my Merc, for example, there is a common problem with the seatbelt connectors/sensors. The light remains on even after fixing this and can only be turned off by a main dealer with their computer system. Which is why mine is still on; finding the time to get such a minor irritation sorted and having to shell out about £50 for the privelege.
I notice there is a sticker on my 9 year old car which says the airbags have to be tested/replaced when it is 10 years old. Sort of ties in with what you have just said RE any future insurance claim.
Against which you have to balance the actual worth of the car. If you consider how much it costs to replace all the airbag componants at the ten year mark it would not be worth it. Bottom line, a nice little way of getting old cars off the road for the minimum hassle.
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