In the final chapter of "Deathly Hallows" ("Nineteen Years Later"), Ron tells Harry that he managed to pass his Muggle driving test by casting a charm on the driving instructor so he would forget about him not checking his mirror (or something like that - going from memory). But electronic devices tend to malfunction in the presence of magical fields, and these days most cars have a high degree of computer control. (If the main part of "Deathly Hallows" takes place in 1997-8, then the "Nineteen Years Later" chapter must take place on 1st September 2017.) Why wasn't the car affected?