Where is the oil sending unit located on a 2002 chevrolet tracker 4 cyl.?

SOURCE: Volvo 850 oil pressure sending unit

It's on the engine, right next to the starter, it has one wire going to it. You don't need to drain the oil. If the light is coming on, you may have bad seals in the oil pan, a fairly common problem, but replacing the switch is a good fisrt step.

SOURCE: locate the oil sending unit on a 2003 6.0 2500HD silverado

You will find it down by the oil filter.

SOURCE: Where is the oil sending unit located on a 2003 Chevy Tahoe 5.3 engine

its in the block behind intake manifold .

SOURCE: oil pressure sending unit

On all 2.0L and 2.4L engines, the oil pressure sending unit switch is located on the engine block, below the exhaust manifold, on the firewall side. On all 2.5L engines, the oil pressure sending unit switch is located on the engine block, below the front exhaust manifold on the radiator side.

SOURCE: location of the oil pressure sending unit 1994

The oil pressure sender is above or below the oil filter, threaded into the side of the engine block.
Hope this helps you.