Where is the rear oxygen sensor located on a 2006 Chevy impala 3.5 engine?

On a 2006 Chevy Impala with the 3.5L engine, the rear oxygen sensor (also known as the downstream O2 sensor) is located in the exhaust system after the catalytic converter. It's typically mounted in the exhaust pipe itself, somewhere between the catalytic converter and the muffler.

Because of the exhaust routing, you'll likely need to get under the car to locate it. It's usually a wired sensor with a connector, and might be a bit difficult to access depending on the specific exhaust configuration. A repair manual or online diagrams specific to your vehicle's year and engine will help pinpoint the exact location.