Employee contributions are subject to an overall individual limit while employer contributions are subject to separate plan limits. You can maximize the employer contribution to the self-employed 401(k) but your employee contributions to the 401(k) at ABC and to your self-employed 401(k) combined for 2019 are limited to $19,000 plus, if age 50 or over, a $6,000 catch-up contribution.
TurboTax's Maximize function for an individual 401(k) does not support the case where you've also made employee contributions to another employer's plan. You can use the SEP Maximize function to calculate only the maximum employer contribution but you'll have to manually calculate and explicitly enter the employee contribution to the individual 401(k) such that you do not exceed the $19,000 (plus $6,000 catch-up) overall limit on employee contributions.
