TurboTax enforces the correct section 402(g) limit of $18,500 for an individual's 401(k) and 403(b) contributions combined. For an individual under age 50 in 2018, the limit of the sum of that individual's Form W-2 box 12 entries (from all employers) with codes D, E, F, S, AA, and BB are not permitted to exceed $18,500.
See IRS: https://www.irs.gov/retirement-plans/how-much-salary-can-you-defer-if-youre-eligible-for-more-than-o...
An individual under age 50 who has one Form W- with a box 12 code D amount of $18,500 and another Form W-2 with a box 12 code E amount of $18,500 has exceeded by $18,500 the amount that that individual is permitted to defer to these plans.
