In the exhaust pipe
The 1990 Buick LeSabre oxygen sensor is located on the outside of the air cleaner housing. The oxygen sensor will be on the back side of the housing.
That should be the Oxygen Sensor
PFM
Crank shaft sensor need replaced or cam shaft sensor
The battery is located under the rear seat cushion on your 2001 Buick Lesabre.
In the glove box.?
Under the back seat
front lower left of timing case cover around oil pan and engine block meet facing firewall
On front cover of engine, slightly above crankshaft pulley.
i believe so
The fuel pump is inside the fuel tank.
The oil filter is located near the serpentine belt and is reached from below the car.