The short answer is that in order to graduate, you must score a 200 on your final PFE which takes place before the start of the second semester in January.
The longer answer is that the passing score for all classes after swab summer is a 200. If you do not score at least a 200, you are placed on remedial probation. There are two levels of probation. Level I is if you score lower than 200 but above your class standard. Level II is if you score lower than your class standard. The class standards are:
4/C (Freshmen): 165
3/c (Sophomores): 175
2/c (Juniors): 185
1/c (Seniors): 200
As you can see, if you do not pass a senior, you are automatically placed on Level II probation. The difference between Level I and Level II is basically how closely they monitor your workout routine. People on Level I have to submit their workout routine on a weekly basis to the PE staff onboard until they pass the test. Level II people are required to attend morning workouts geared to getting you in enough shape to pass. They're not fun.
The other caveat is that once you are placed on probation, you must pass the PFE twice in order to get off of probation. So, if you're on Level I probation, you must score a 200 twice before they take you off. If you're on Level II probation, you have to pass above you class standard twice, then you are moved up to Level I probation where you then have to get a 200 or above twice before you're taken off. PFEs during academics are conducted during lunch periods so then you miss out on that as well. So, if you're on Level II probation, you will at a minimum take the PFE 5 times rather than just the once a semester deal everyone else goes through.
Moral of the story, workout and avoid probation. The PFE sucks, especially on an indoor track w/ little ventilation, but it sucks less taking it once than taking it 5 times. I had classmate get kicked out the WEEK of graduation for not being able to make weight/pass the PFE. You don't want to be that guy.