How do I resolve this error: AMT dep allowed is too large. For disposition calculations, depreciation cannot exceed business basis.

The SmartCheck message is saying that the depreciation amount is too high in comparison to what the vehicle is worth. The prior AMT depreciation would be the same as the prior regular depreciation if the depreciation was calculated by using the standard mileage deduction. 

Try this first:

1. Delete the vehicle. 
2. Add it back in with its original service date. 
3. Calculate your estimated depreciation per year based on miles used for business. You may need your Depreciation Reports from last year or see this link for help: IRS Pub 463 Depreciation adjustment when you used the standard mileage rate.
4. If you don't have prior depreciation reports, that's OK, use the defaults presented in TurboTax. If you've had the vehicle longer than 5 years, it would be fully depreciated under both the regular and AMT methods.

Other options: 

• Go back to the sale of vehicle and delete any numbers in the AMT section.
• In Smart check, when the worksheet is displayed, right click on the field (Line 51 and/or Line 52).  From the dropdown menu displayed, select "Override". You should then be able to enter any number that you want. However, do not enter an amount greater than the depreciable basis of the vehicle. If you've used the vehicle more than 5 years, the basis is zero.

If you're using TurboTax for Desktop, you may be able to manually fix this using Forms Mode.

1. Open your return and click the Forms icon in the TurboTax header. 
2. In the list of Forms in My Return on the left, scroll down and look for Car & Truck Wks [your vehicle]. 
3. Click the form name to open it in the large window. 
4. Click the Errors icon above the list of forms to open a message box below the open form.
5. Scroll down through the worksheet and look for fields highlighted in red.
6. Click the red field to see an explanation of the form error in the footer.
7. To track the source of the number in the box, or read more about the field, right-click the box and choose either Data Source (where the number came from) or About... (what should be in the box).
8. You can edit any number in a blue font. Black numbers are calculated and cannot be changed.
9. With the sale of a vehicle, you may need to revise the numbers on line 36(i) and/or Line 37.
10. Once all the form errors are fixed, click Step-by-Step in the header to return to the main screens.
11. Now run SmartCheck again to confirm the error has been resolved.