Hi Edward, 

Without knowing all the details and seeking legal advice we couldn't comment on legality here, but I am surprised to hear that the traction motor (I assume this is a plug-in hybrid you have) is not covered by a warranty. A used car warranty offered by a dealer is quite different to that of a new car warranty and it should clearly outline what is and is not covered. If you did not receive such a document, or the dealer cannot show a standard warranty agreement document, then you may have a case, but if you bought the car and the warranty information clearly excludes the traction motor then I don't think you'll have any joy in getting a replacement under warranty. 

Either way, it's worth seeking professional legal advice on the matter once you have all the details to hand.