I financed a car in april 2017. can i write off sales tax?

Yes, as an Itemized Deduction on Schedule A.  Make sure the amount you include matches what is on your paperwork from the seller.

Here is where to enter it:

1. Once you are in your tax return, click on the “Federal Taxes” tab 
2. Next click on “Deductions & Credits”
3. Next click on "jump to full list" or “I’ll choose what I work on”
4. Scroll down the screen until to come to the section “Estimates and Other Taxes Paid ”
5. Choose "show more", then Sales Tax (start/update/revisit)
6. Choose - continue to sales tax and choose "Easy Guide"
7. Enter your state sales tax information (If your state sales tax information is already entered you will need to edit it to enter your major purchases information.)
8. On the screen that says Major Purchase - select "yes"
9. Enter your vehicle information and sales tax here on the next screen.