Please enter both of the box 12
entries into the appropriate lines in TurboTax on the W-2 input page. It does
not matter in which order you enter them. The DD code is for the amount of your
employer's contribution to your health care, and the D code is the amount that
you contributed to your 401(k) plan - so two different things.
If necessary, click on "Add another row" to add more space for
more box 12 entries.
If you have questions on what any other codes in box 12 mean, please see this TurboTax FAQ.