If you have an automatic gear box and select a gear directly. Ie. 1st,2nd or 3rd, will it still go into that gear if the road speed is too high?

Was on the motorway and wanted it to kick down into 3rd, but will not do this unless under 75mph, so manually seclected the gear, but was just wondering what would have happened had I pulled it back to 2nd by mistake?

 

Every auto that I have driven will treat the selection as a pre-selection and will not complete the change until the road speed drops to a pre-determined level.

 

That is the kind of answer I was hoping to hear.

100mph is 6000rpm in 3rd, so dropping back into second at this point could spell real trouble for the engine.