Where is the oil sending unit on 1998 Buick Ultra?

The oil sending unit on a 1998 Buick Ultra (assuming you mean a Park Avenue Ultra) is located on the oil pan. However, pinpointing the exact location without seeing the engine is difficult. It's typically on the side of the oil pan, often near the front, but it can vary slightly depending on the engine (3.8L Series II is the most common in that year).

To find it:

1. Consult a repair manual: A Haynes or Chilton repair manual specific to your 1998 Buick Park Avenue Ultra will have diagrams showing the precise location of the oil pressure sending unit. This is the best and most reliable way to locate it.

2. Visual Inspection: Once you're comfortable working under the car (and have properly supported it!), look at the bottom of the engine, focusing on the oil pan. The sending unit is usually a small, electrical connector with a single wire going to it. It may have a single or sometimes two-wire connection.

3. Feel around carefully: Once you've visually identified the general area, carefully feel around the oil pan. The sending unit will be a threaded fitting, similar to a sensor. Be cautious as the oil pan is hot after running the engine.

Important Safety Note: Always ensure your vehicle is parked on a level surface, properly secured on jack stands (never rely solely on a jack), and the engine is completely cool before attempting any work underneath. Wear safety glasses and gloves. If you're not comfortable working on your car yourself, take it to a qualified mechanic.