Where is O2 sensor on a 2004 Ford Taurus?

The O2 sensor on a 2004 Ford Taurus is typically located in the exhaust system. There are usually 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 found after the catalytic converter. You may need to lift the vehicle for better access, especially to the downstream sensor.