2002 Focus Won't Engage In Park

I have a 2002 Ford Focus ZX3, and it won't engage in park, but it will shift into park. We've detached the shifter cable, but it still happens when it's detached. My grandpa also said that it's not the linkage. We don't really know where to go from here. Also, it will go into park if it's shifted into reverse, and then without pushing the break, slamming it into park. Thanks in advance.