[gschotland]

The O2 sensors look roughly like big spark plugs with about a foot of wire coming out of the top (photo attached). They screw into the side of the exhaust pipes near the catalytic converters; for a '99 I believe you have 2 per side. It's helpful if you have a special O2 sensor removal wrench (spanner) to provide good leverage without slippage. Such a tool should be available at any auto parts store. Attached is a photo. Notice it's usually meant to be used with a 1/2" socket wrench.

To access the O2 sensors you'll need get the rear of the car high enough to easily slide yourself underneath. A large floor jack along with a pair of high quality, stable jack stands will work well and should be safe. Slide underneath and remove the plastic belly pan closest to the engine. Look at the exhaust pipes and catalytic converters and the O2 sensors will be obvious. Carefully undo the clips at the end of the sensor wires, then use unscrew the sensors from the pipes. The sensors can be very tight so you may need to tap your socket wrench with a hammer or use a piece of pipe to get enough leverage to break it loose. Next, swap them left to right. Installation is the reverse of removal.

Invest $60 in a Bentley service manual. Use it for one project (like this) and it's paid for itself. And yes this is an easy project.

Let us know how the swap worked out.