Hi there,
Just had my engine light checked today on my 2002 sc430. The code showed an o2 sensor, possibly. There are 4 in total. Bank 1, which are just below the manifold (exhaust manifold), bank 2, which are mid positioned to the doors, under the car. I take it yours are bank 1. To access these both covers under the engine bay must be removed. I am in the uk so my car is right hand drive. Therefore on the passenger side three heat shields have to be removed.The bolts on these are very delicate, especialy the 3/8 fitted just above the catalist.Once removed however the sensor can be removed with a plumbers tap wrench. The drivers side is much easier, and if the connector ( wiring) is coated in oil, probably from a leaking powersteerig pump, you may only have to change the fuses, after cleaning the wiring and sheathing it to protect from further saturation. This is a very poor set up, especialy from this premier japanese car. Lexus take note.
Hope this helped, Asif