Might the car only have 3 O2 sensors?

[Jack from Charlotte]

My wife's '98 Acura RL is showing a check engine light. I go to Auto Zone and get....(I think) P0141 which is downstream O2 Sensor in bank 1. OK. I replaced one on my Taurus before. The "upstream" sensors on this car are easily seen under the hood. Almost in the place you'd find a spark plug. I pull the car up on my ramps and look underneath. The only sensor I see is way back past the center of the car behind the cat. I go from the mufler forward and see no other wire or anything going into the exhaust system. So does this car only have 3 O2 Sensors?

 

[T-Keith]

OBD-2 requires at least 2 O2 sensors, one before and one after the CAT. Some manufactorers choose to use two primary O2s(one for each bank) and some use two CATs also. So you can have 2, 3 or 4 O2 sensors.

-T