Dear sir
In reference to the o2 sensor being weak. I can see readings of o2 voltage and fluctuations. Is there a particular pattern or sign that its weak. Without replacing it. I'm in that smog check paradox and mayhem. All my sensors cleared and passed at the 90 mile mark. Except evap and secondary air. Filled tank bellow full evap cleared at about 120. Now at325 miles secondary will not clear. I have tested power and function on cold start and blows air like a dam hair dryer ,works fine . also cleaned out carbon deposits replaced hoses.
Now what? Do you suggest

2000 e320 300k mi..