DateTimeAxis MinorStep Problem

I am trying to plot some data for a month, so I set the MajorStep to week and the MinorStep to Days, like this, and it's working well.

DateTimeAxis1.IntervalType = DateTimeIntervalType.Weeks;
DateTimeAxis1.MinorIntervalType = DateTimeIntervalType.Days;
DateTimeAxis1.MinorStep = 1;
DateTimeAxis1.MajorStep = 7;

But If I change the IntervalType to Auto, like this, It shows the MajorStep as Weeks, but it doesn't show the MinorStep (days) interval at all

DateTimeAxis1.IntervalType = DateTimeIntervalType.Auto;
DateTimeAxis1.MinorIntervalType = DateTimeIntervalType.Days;(
DateTimeAxis1.MinorStep = 1;