Why does my 2000 Nissa Quest GXE keep cutting off while driving?

What is your question?

OK, so when I drive my 2000 Nissan Quest GXE, it will randomly cut off. I lose power steering and the brakes become very hard to press. I know there is an oil seal that neds to be replaced, (it's the back one), and I've had an auto parts store run a diagnostic on it, and the codes that read are the knock sensor and two others I can't currently remember, but was told were not relative to it cutting off. The fuel pump is fine, and so is the battery. Any help would be greatly appreciated. Thanks.