If a part of your car’s diminished value was not reimbursed, you can write it off and deduct it from your taxes as a property loss. Use IRS Form 4684 and the Schedule A section of Form 1040. Although you won’t need it for your tax return, keep your documentation, because you may need it if you get audited. The documentation should include the following information:
Dollar amount of the property loss
Reimbursement amount, if any
Proof of legal ownership of the vehicle
Accident details, including fault