When your employer prepares your W-2, your employer reduces the amount that would otherwise be in box 1 by the amount in box 12 with code D. The amount that you enter with code D into box 12 of TurboTax's W-2 form only potentially affects the amount you are eligible to receive as a Retirement Savings Contributions Credit. Since you apparently do not qualify for this credit, changing the code D amount will properly have no effect on your tax return.
