The AMT depreciation amount is usually the same amount as regular depreciation amount TurboTax calculated.
Try entering that amount or entering $0.
If you are trying to enter a new business vehicle and indicate you stopped using an older business vehicle, this can be reported as a 'like kind exchange'.
Here's more info:
https://ttlc.intuit.com/replies/3301982
Edited 3/5/2018 12:58 pm