Answer:
Plastic part, probaly rusted in so it broke off. If you have room - heat up a suitable piece of flat metal, red hot. Press it into the plastic, it melts easily. When it cools twist it out with a wrench.
If no good, drop oil pan and try to knock it out from inside. If metal part fell into engine, you will have to drop pan a few inches to magnet it out.
I'm at that stage with my 2003 Jeep Liberty.
Sounds promising. However my end result was its a metal casing with some plastic crap in it and a magnet at the bottom. I wound up using a tree style tip on a dremel tool and then used a drill bit in the dremel around the magnet and then just slid it out after i had removed the majority of the sensor. This entire process took about 2.5 hours
Another way to get this out is to grab it with locking vise grips and wiggle it back and forth a bit to loosen then pry it out with a big screwdriver.