Where is the oil pressure sensor on 2003 impala 3.4 liter engine?

The oil pressure sensor on a 2003 Chevrolet Impala with the 3.4L engine is located on the rear (back) of the engine block, near the oil filter. It's often a small, usually one-wire sensor. You'll likely need to get underneath the car to see it clearly. A shop manual or online diagrams specific to that year and engine will help pinpoint the exact location.