For a while, I kept getting the front O2 sensor sweep from full rich to full lean slow over and over and over again. What an engineering friend did was explain why it failed, and how to fix the problem.

Since I already spelled it out in length already, and it was deemed not fit to archive, I will keep that part as short as possible, and go to the fixing part.

If it is determined that an O2 sensor is not functioning properly, often it is because of contaminants on the sensor itself, usually from the combustion of low quality gasoline.

Now, to clean the sensor off, remove it from the exhaust line, heat it with a torch till it glows orange. Keep it glowing orange for atleast 2-3 minutes. Then, wait till it cools enough so that should you spray non-chlorinated brake cleaner on it, that it doesn't sizzle. Then, using some non-chlorinated brake cleaner, spray it down. At this point, you will see lots of black crud coming out of the little seams in the O2 sensor guard. Then, wait a couple minutes, and blow torch it again.

If you specifically have the slow sweep, what you might also want to do is open up one of the seams.

I did this to my front O2 sensor about 1.5 months ago. Before then, I would pull the code every couple weeks. After a while, it started pulling codes every other day or so. And since I did this, I haven't pulled a code in 1.5 months.