Spark plug anti-foulers to cure code P0421

[glenn_dam@yahoo.com]

I keep getting the pesky code P0421 on my 2000 MPV. I've read in multple sites that you can use spark plug anti-foulers on the post-cat O2 sensor to fool the system and cure this code from coming back. First, I'm assuming they're talking about the pre-cat, as there do not appear to be any sensors after the main cat. Second, I can see two possible sensors that I can reach that appear to be after the pre-cat. The one furtherst back is in the top of the pipe, which is a few inches behind the oil pan plug (the pipe that gets sprayed with oil when you try to change the oil yourself!). The other one is in a horizonal pipe that is coming over from the driver's side. Since these are a real pain to remove, can anyone confirm the correct sensor to install into the anti-foulers? Also, is it possible to unscrew the sensor without disconnecting it? The connection is pretty touch to reach in the back of the engine. I can feel it but can't see it so I'd rather leave it alone if possible. Thanks for any advice!