Detailed answer — What Illinois law says and what typically happens

1. Who matters: your role and how the car was titled

The outcome depends mainly on:

• Whether the car was part of the probate estate or owned outright by your dad at his death.
• Whether you were acting as a personal representative (executor or administrator), a trustee, or acting as a private individual/beneficiary.
• Whether you had court authorization (or statutory authority) to sell the car and whether you followed required procedures.

Under the Illinois Probate Act, personal representatives and trustees owe fiduciary duties to the estate and beneficiaries. See the Illinois Probate Act (755 ILCS 5/) for the general framework and the court’s power to supervise fiduciaries: https://www.ilga.gov/legislation/ilcs/ilcs3.asp?ActID=2106&ChapterID=60

2. If you were the personal representative or trustee

Fiduciaries must act in the estate’s best interest, follow the will (if there is one), and avoid self-dealing. Typical issues the court will consider when a sale is challenged:

• Did the fiduciary have legal authority to sell the vehicle? (Authority can come from the will, statute, or a probate court order.)
• Was the sale commercially reasonable? Was there a fair price or an appraisal, and was the process transparent to beneficiaries?
• Were sale proceeds handled properly (deposit to estate account, used to pay debts/expenses, and ultimately distributed to beneficiaries)?
• Did the fiduciary personally profit improperly from the sale (self-dealing) or convert estate property?

If the court finds a breach of duty, available remedies include ordering an accounting, surcharging the fiduciary (making them pay back loss or profits), ordering return of the car (if possible), removing the fiduciary, or requiring other equitable relief.

3. If you were just a sibling/beneficiary who sold the car

If the car was not in the estate (for example, it was titled in your name or your dad transferred it to you before death), you have more protection. But a sibling who believes the car should have been part of the estate or that you converted estate property can still file a claim. The court will look at title, transfer documents, timing, and intent.

4. Typical steps your sibling can take

1. File an objection in the probate case or begin a new probate petition asking for an accounting and relief.
2. Move to remove you as personal representative or trustee (if you hold that role) and request a surcharge or repayment.
3. Bring a civil claim for conversion (wrongful taking), breach of fiduciary duty, or unjust enrichment.
4. In rare cases, refer the matter to law enforcement if theft or criminal conversion is alleged—but criminal charges are decided by prosecutors with a higher burden of proof.

5. Evidence the court will want to see

• Title records and transfer documents (title certificate, bill of sale).
• Probate filings showing who is personal representative or trustee and what authority they had.
• Receipts, appraisals, advertisements for sale, and bank records showing how sale proceeds were handled.
• Communications to beneficiaries (notifications, accounting statements, consent forms).

6. Possible outcomes

• No action if you had proper authority and documentation.
• Court-ordered accounting and documentation to explain the sale.
• Surcharge or money judgment if the sale undercut estate value or produced improper personal gain.
• Return of the car if it’s still in a recoverable state and the court orders rescission (rare if the car was sold to an innocent third party who bought in good faith).
• Removal as fiduciary and replacement by another representative.

7. Timing and practical considerations

Probate proceedings can take months to years, depending on complexity. Acting quickly to gather paperwork and communicate with other beneficiaries often improves your position. Courts favor transparency—documenting why you sold the car, how you reached the sale price, and how you handled the money reduces the risk of an adverse finding.

Helpful hints — Steps to protect yourself and what to do next

• Keep all documents: title, bill of sale, invoices, appraisal, ads, and bank deposits showing where sale proceeds went.
• If you acted as personal representative, make a written record explaining your decision to sell (why a sale was necessary, how you marketed it, and why price was reasonable).
• Provide beneficiaries a clear accounting early. That often prevents disputes from escalating.
• If you sold the car to a third party, collect and preserve buyer contact information and any transfer paperwork.
• If a sibling threatens court action, consider offering a voluntary, signed explanation and copies of records before things escalate—sometimes disputes settle quickly with clear records.
• Consult a lawyer experienced in Illinois probate and fiduciary law if you receive a formal complaint, petition, or subpoena. Even a short consult can help you understand exposure and options.
• Act fast to correct honest mistakes: if you misapplied proceeds, returning funds or correcting the distribution may avoid a bigger problem.

Where to read the law

The Illinois Probate Act contains the statutory framework for fiduciaries, probate administration, and court supervision: https://www.ilga.gov/legislation/ilcs/ilcs3.asp?ActID=2106&ChapterID=60