First, be sure that your 12/31/2017 balance sheet agrees with the balance sheet in last year's tax return.
Next, check book versus tax depreciation. If they are not the same, were the correct fields filled in TurboTax Business to allow the depreciation to be reconciled?
Look for P&L line items that are not tax deductible, for example: fines & penalties, charitable contributions in excess of limits, etc. Also look for non-taxable income. These items also have to be reconciled.