If I sell my car off at a loss, can I write that loss off against my income to save on tax? Does it matter if the car was used just for personal leisure use, or if I used the car to generate business income? (e.g. travel to work, to attend education seminars, etc.)
While you'd need to pay tax if you realized a capital gain on the sale of your car, you generally can't deduct any loss arising from the sale of "personal use property". Cars are personal use property.
Refer to Canada Revenue Agency – Personal-use property losses. Quote:
[...] if you have a capital loss, you usually cannot deduct that loss when you calculate your income for the year. In addition, you cannot use the loss to decrease capital gains on other personal-use property. This is because if a property depreciates through personal use, the resulting loss on its disposition is a personal expense.
There are some exceptions. Read up at the source links.