Where is oxygen sensor for a 2005 Ford Freestar located?

The oxygen sensors on a 2005 Ford Freestar are located in the exhaust system. There are typically two sensors: one upstream (pre-catalytic converter) and one downstream (post-catalytic converter). The upstream sensor is located on the exhaust manifold or just before the catalytic converter, while the downstream sensor is located after the catalytic converter. To access them, you may need to lift the vehicle and work under it.