On 28/04/2018 21:26, dennis@home wrote:
On 28/04/2018 16:25, John Rumm wrote:
On 28/04/2018 14:46, dennis@home wrote:
On 28/04/2018 12:54, The Other Mike wrote:
On Fri, 27 Apr 2018 22:46:50 +0100, "dennis@home"
wrote:

Do you think its legal to drive a car that you know will fail the MOT?

Yes it is legal

They can prove you know if the fault has been cleared without the
diagnostics being run.

Would love to know how anyone would actually perform this action

Unless you know why it came on you don't know if the
airbag will deploy when it should or if it will deploy when it
shouldn't. You would look pretty stupid if it went off while you were
doing 70 on the motorway or leaning over to clean the screen.

The built in precautions to prevent accidental deployment of an airbag
also ensure intentional deployment


Its faulty, the light is/has been on, so what you just said doesn't
apply or even make sense. That is the whole point, you do not have a
clue as to what will happen when the system has/is indicating a fault.
It may fail to go off when it should, it may go off at some random
point, it may even work as expected.

I would expect any safety critical design to fail safe...

For example I had a dodgy sensor on one car with ABS. If you hit a
pothole with the rear offside wheel it would cause the ABS warning
light to come on. At that point the ABS system as a whole was then
inhibited, and the breaking system reverted to a normal non ABS one. A
design decision, that elected to possible disable the breaks entirely
on detection of a fault, would hopefully not get through a design review!




Design covers faults that they can predict, not ones they can't.

That's not acceptable for safety critical system. Either it works as
intended or its locked out from operation.

So a safety critical system may identify that there is a fault but may
not be able to safely "fix" it.

It may not be able to fix it, but it can cease doing what is required to
keep it active. (the hardware default should be to disable it, like any
safety critical system)


--
Cheers,

John.

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