What is the O2 sensor on a 2003 Ford Expedition?

Answer 1

Here is the oxygen sensor, and their location designations explained: They are screwed into the exaust system at various points. Some people say that there are 4 oxygen sensors, but technically, that is not correct. Only the front 2 are considered oxygen sensors. They are screwed into the exaust pipe, one on each bank, after the exaust manifold, but before the catalytic converter. Sometimes they are screwed directly into the exaust manfold itself. The other 2 are actually called catalyst moniters. They are oxygen sensors, but they serve a different purpose. They moniter the activities of the catalytic converters, thus the name, catalyst moniters. They are screwed into the exaust one on each bank,after, or downstream, of the catalytic converters. On a 4 cyl engine, there are only a total of two such sensors, the one in front of the catalytic convertor is the O2 sensor, the one behind the cat is the catalyst moniter. The location names for them are as follows: On a 4 cyl, the front is called "bank 1 sensor 1" and the rear sensor is called "bank 1, sensor 2." On a V6 or V8 engine, the passenger's side bank on a forward facing engine, or the bank closest to the firewall on a transverse mounted engine, is bank number 1, so the forward sensor on that bank would be "bank 1, sensor 1." The driver's side bank(forward mount engine), or front bank(transverse engine) would be bank number 2, thus the forward sensor on that bank would be "bank 2, sensor 1," and the rearmost sensor on that bank would be "bank 2, sensor 2."