Oxygen (O2) & Sub-Oxygen Sensors: Notes
WARNING: This page is about a different car, the 1994 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
To ease removal of O2 sensor and/or its mounting bolts from exhaust pipe/manifold, it may be necessary to apply penetrating oil to threads. Also run engine a few minutes to heat exhaust system to about 120°F (48°C).