The general advice we have received is that if your costs exceed your income from sharing your car, then you can offset the loss against your salary or other income. You may wish seek advice for your own circumstances.
Most people share their car simply to offset the cost and reduce waste of a car that they would own anyway, and don’t intend to earn a profit. So it’s not unusual for a car’s income to be less than the costs that the ATO allows you to claim.
What income you need to declare in your tax return
What costs you can claim in your tax return (including depreciation)
How to apportion your expenses between personal and income-producing use
Tax requirements for sharing a car that is owned by someone else or jointly owned