Outstanding finance is common and dealers are set up to handle it. They will usually ask for your agreement number and lender details, then obtain a settlement figure that is valid for a set number of days.
Your part-exchange valuation is then compared with this settlement. Positive equity can be used as a deposit on your next car; negative equity may need to be paid by you or, in some cases, refinanced into the new agreement if the lender approves.
You should never try to hide existing finance. The lender normally has a legal interest in the vehicle until it is settled, and selling without clearing it properly can cause serious problems later.
This page is neutral and factual. It is not legal or financial advice; always confirm details with the dealer and finance provider.