The modern car or truck has lots of sensors to tell the vehicle's computer how the engine is running, and tune accordingly. One of these is the oxygen or O2 sensor, which detects the amount of oxygen in the vehicle's exhaust system and adjusts the fuel/air ration at the heads accordingly. If these sensors go out, you'll see a "check engine" light on your dash until they're replaced, and your Jeep Liberty will run sluggishly. This isn't a fun job, but it can be done in about an hour with the right tools.
Lift up the vehicle using the jack and place it on jack stands. Make sure the vehicle is secure before you crawl underneath it.
Locate the O2 sensors on the exhaust. They're about 2 inches long, and have a wire pigtail sticking out of the end. These are also the only sensors on the exhaust, and the only wiring that's near the exhaust at all.
Unplug the O2 sensor from the vehicle wiring harness using your hands.
Remove the O2 sensor using the 3/8-inch ratchet and the oxygen sensor socket. Then thread the replacement O2 sensor in place and tighten it down using the 3/8-inch ratchet and the oxygen sensor socket.
Plug the O2 sensor back into the stock harness using your hands. Repeat the process for the other O2 sensors in the exhaust, then lift the vehicle back up and remove the jack stands using the jack.
