It is very electrical load sensitive, I was running a dash cam plugged into an adapter with mixed amperage, if plugged into the higher power (2.4 A) iStop will not work, on the lower powered port it does.
Get the Fuel Economy Monitor up on the centre display, across the bottom of the first page are 3 icons which will tell you why iStop is not possible: battery, climate control and engine. The only time iStop doesn’t work on my 2019 is engine cold, demisting set or I’ve just rinsed the absolute bajeezus out of the engine (I think this is some kinda of protection thing to keep oil circulating?)
My guess would be low battery state of charge from either being stood or the battery being on its way out.
You might also find the adapter was putting out rf interference and confusing the iStop, and adding a couple of suitable ferrite beads close to it on the In and Out wires might remove the problem.
Or they might not…
Sometimes you can be sat at a red light with the engine running, and it only takes turning the heater dial down a bit for the iStop to kick in and the engine go off. I think this is because if the car interior is still cooler than the level you’ve selected, it will prioritise warming you up over turning on iStop. Turning the heating down will tip the balance in iStop’s favour.
Similarly, having the air control set to demist - which automatically turns the AC on will also stop iStop from kicking in.
Heated seats don’t stop it from kicking in, but will add to all the other factors in whether it will turn the engine off and how long it will stay off for.
When I fitted a dashcam, I noticed a reduction in how long iStop will stay on for, but it still does work, with the heated seat on and lights and heater (as this morning).
Wheels need to be straight for Istop
to work too. Istop uses heat and high compression to restart using a small spark - it’s very fast and doesn’t use/knacker the starter motor it’s a brilliant system.
It does use the starter motor to assist, unless it’s one of the e-SkyActiv-X cars, which use the Li-ion hybrid battery and the motor-generator (in place of the alternator) via the drivebelt. They really do restart silently.
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