Lines 51 and 52 of the Car and Truck Expense Worksheet report the depreciation you were legally allowed to claim on the vehicle under IRS regulations. These numbers may differ from what you actually claimed, but the TurboTax program would have calculated your legally allowable depreciation when you entered the vehicle as a business asset.
Publication 946 (2019), How To Depreciate Property
If it is showing up as a gain on schedule 1 line 4 and you had fully depreciated the vehicle, you must have reported a positive value for the "Sales Price" (Line 44 of the Car and Truck Expense Worksheet)
You will have to review your entries in the Business Assets interview, where you reported the disposition of the vehicle, and make sure the "Sales Price" is "0".
