While we hear of the TARDIS having engines that are implicitly essential to it working, we’ve also see a TARDIS work without the rest of the machine.
“The Doctor’s Wife” and “Inferno” show that a TARDIS is capable of operating as just the console, which would seem to imply that they’re just a power source to allow the console to do its thing and move the whole ship around, or to allow for the pilot to do silly things like tow an entire planet one second out of phase.
My take, informed mainly by The Doctor’s Wife, is that while a TARDIS console alone can move through time and space, it’s a bit like driving a card without a windshield, exhaust system, shocks and brakes. It may get you where you’re going, but the odds of you experiencing harm increase greatly.