17 volt electrical system

That's not an easy one.

Unless your car is equipped with a regen braking system, rolling downhill doesn't enter the equation neither does the freefall.

Lightening however could be a determining factor.

Your signature says, "Always check info with a digital multimeter." But I don't recommend you do so in this case.

An average bolt of negative lightning carries a current of 30-to-50 kiloamperes(kA), although some bolts can be up to 120kA, and transfers a charge of 5 coulombs and 500 megajoules (enough to light a 100 watt light bulb for 2 months). However, it has been observed from experiments that different locations in the US have different potentials (voltages) and currents, in an average lightning strike for that area.

So when you said that you're driving off a cliff, what part of USA would that be in? It will aid us in being more precise.

It also says, "I promise to be good."   

(Can you tell that it's a slow day at work?)