Can I use mortgage loan for new car?

My husband and I are in the process of buying our first home, we also have a car that we would like to trade in for something newer. Is it illegal to bump our mortgage loan up by $10,000- $15,000 and use it to buy a pre-owned car? The car would be payed off at the dealership with the loan, so it would be 'payed off' immediently, as in, we will only have a few extra dollars a month added to our mortgage. I see it as consolidating car loan and mortgage- is this a good idea?