service schedule up to date.

yes its in warranty. dealer already replaced sat nav unit,fault still shown with replacement, then they referred back to toyota tech and thats when i was told they would take no further action.

Take it back to the dealer. It is faulty, it is under warranty. You therefore expect it to be fixed, unless the warranty specifically excludes electrical items, or says words to the extent of "We'll only fix it if we can be bothered".

Assuming you're working through the same dealer you bought it from, do remember that your contract is with THE DEALER. Technically, in law, it is nothing to do with Toyota GB.