A manual is required if you want to play effectively. Factory is best but pricey, Chilton's/Hayne's are about $20. I have both C&H but covet a factory. There is an on-line version which seems very good but it is $20 a year for 1 vehicle and not as user friendly as a book. Sorry, I don't have the link.
Raise the front end, slide your head under the van, find the cat, now go up through the channel and it's in the pipe above the cat, second one is in pipe after the cat. Did I mention this is a tight fit? Well...I guess I just did.
If it turns out you have to replace, get an O2 Sensor socket (has a cut out side so the wires can go through it) or cut the wires, you will still need the O2 socket to install a new sensor. Put PB Blaster on the threads and tap the pipe (vibrations help break rust/corrosion). Wait 24 Hours and repeat. Wait again 24 hours, spray some more PB then take it for a drive, so it heats up. Attach the O2 socket (wear gloves), an extension, put a bar on the extension and turn from outside the front compartment. It should come, but they can be a bear to get off sometimes. It may also make a screeching noise, but that's ok.
When re-installing make sure you add additional anti-seize as there isn't enough on it from the factory. I get them tight and turn about another 1/4 turn, some peeps torque them.
Good luck with your project!
