Correct. As one firm describes it:
For a corporation, employee salary deferral contribution must be done through the payroll.
Using a W-2 form, an employee of a C Corporation or S Corporation can make a deferral contribution at any time within the year when the income to be contributed is earned. Timing of the contribution typically will depend on the corporation’s payroll structure.
If the corporation uses a payroll company, a deferral contribution generally will be deducted from the employee’s paycheck. If the company does not use a payroll company, an employee can elect to make a deferral contribution at any time during the year.
The Department of Labor’s safe harbor guidelines stipulate that a deferral contribution to a Solo 401(k) account is to be made within seven days of the date on which the employee elects to make the contribution.
An employee who elects to make a deferral contribution in a given pay period — on Dec. 30, for example — should be sure that his or her paycheck for that period is sufficient to cover the contribution.
(Technically, both deferrals and profit sharing contributions can be deposited by filing deadline + extension)
Retired, no salvage value.