I need to know how to record the sale of a vehicle against a loan. The vehicle is tied to the loan of the business.

I'm going to assume by loan, you mean you loaned the sum necessary to buy the business.

If that is the case, then
calculate and post partial year depreciation on the vehicle
then create a loan asset account, due from [name] or something

journal entry
debit vehicle fixed asset account for the total in that account, credit due from account
debit due from account, credit vehicle accum depreciation account for the balance in that account

debit due from, and credit all other assets that were part of the sale
( if inventory items were involved do not use a journal entry, instead use inventory adjust, set the adjusting account to the due from account and set the qty of all inventory sold to zero)

the deposit you received, set the source (from) account to the due from account

I am going to go ou ton a limb and say you sold business with vehicle all on owner financing, you holding paper? Otherwise why would a payment for something you own free and clear be even tied to a loan?

And by "outright" is or was this vehicle fully depreciated?  Since you owned it outright there would be no bank loan you would have to reduce by making any payment to a bank.  If it had become encumbered as collateral for a business loan you had in place prior to selling the business then you did not own it free and clear on date of sale.

If the loan is all you owing the bank should it not have been eliminated entirely when you sold the business?  What did you do with those proceeds? Was there not enough to clear off the entire loan?

Perhaps, I listed too much information in the original post.  Here is the short version:  

When the business was purchased, the vehicles were tied in as part of the sale of the business.  We sold one vehicle.  Our bank is posting the sale of the vehicle against the loan for the business. Our loan amount should decrease.   I am not sure how to show that in QB online.  I see in our bank register the deposit from the sale and it also shows a payment, meaning the money left the bank account.  (Rightfully so, because it went against the loan.) However, QBO is not showing a decrease in the loan.