Silkstonemik4,
as someone who works in the Automotive manufacturing new model launch, the shutdown month is used as the period to bake model year and new model launch changes to production lines.
To change model years and release new models requires a lot more than just swapping parts online, there will be the installation of new equipment, new fitting stations, changes to build patterns.
The European summer closure is the whole of August and that is when these changes occur, with September used as a ramp up tine to find any issues with build.
if there are parts changes,which there will be, suppliers work in a 12 week schedule 4 weeks fixed, 4 weeks tentative and 4 weeks raw material. To run down stocks,bas no manufacturer wants to be left with a lot of stock, these suppliers are given a final date for supply, and they too will be removing tooling to either replace or modify that tooling for the new MY, so that’s why production stops.