Took the new Yeti out to Lacock Abbey yesterday,

went straight there nothing out of the ordinary.

Coming back the Stop Start operated twice at

traffic lights and once waiting to turn right on a

roundabout. Came down through Bath but it did

not operate at all at any of the traffic lights.

It does say it can and will operate like this, why?

(The first time it stopped my heart leapt into my mouth

then I remembered the Stop Start)

Did you have a significant power drain such as heated seats, air con with high fan headlights etc......they are driven by the battery state and drain on it.

Or DPF regeneration taking place?

That's normal it will only stop if the battery will start the car wait till you are stopped with the stop start and it starts up on its own

I think they're potentially dangerous and an example of emissions targets out of control.

Ours has failed to start , sounding an alarm instead (bong) with a message telling me what I need to do BUT what I HAD done!

I can imagine someone panicking and confused getting into trouble, unable to work out what to do.

It defaults to being active unless deactivated.......just to get emissions certification.....madness.

What was the Ambient Temperature when it happened yesterday, near 0*oC ?

That's normal it will only stop if the battery will start the car

There are other reasons too (including the DPF regen reason above).

Our new Superb (150 TDI) has Stop-Start, and also has a menu where you can see the reasons why SS didn't kick in.

Most common reason is "risk of windscreen fogging" or something like that.