The oil pressure sending unit on a 2004 Chevy Silverado 4.3L V6 is located on the driver's side (left) of the engine block, near the oil filter. It's a small, usually single-wire sensor. You might need to use a wrench or socket to remove it, and you'll definitely want to have a drain pan handy to catch any oil that might spill. Because it's near the oil filter, getting to it might require maneuvering around the filter and associated plumbing.
Important Note: It's always best to consult a repair manual specific to your vehicle year and model for precise location and removal instructions. Pictures in a repair manual will be invaluable in this process.
