Here is the low-down on oxygen sensors, and their location designations explained:
sensors are screwed into the exhaust 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.
oxygen sensors are screwed into the exhaust pipe or directly into the
exhaust manifold, one on each bank. Because they are in front of the
catalytic converter, this is often referred to as 'upstream'
other 2 are actually called catalyst monitors. They are oxygen sensors,
but they serve a different purpose. They monitor the activities of the
catalytic converters, thus the name, catalyst monitors. They are screwed
into the exhaust one on each bank, after, or downstream
, of the catalytic converters.
a 4 cyl engine, there are only a total of two such sensors, the one in
front of the catalytic converter is the O2 sensor, the one behind the
cat is the catalyst monitor.
The location names for them are as follows:
- On a 4 cyl, the front / upstream is called "bank 1 sensor 1" and the rear / downstream sensor is called "bank 1, sensor 2."
- On a V6 or V8 engine:
passenger 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 / upstream sensor on that bank would be "bank 1, sensor 1."
driver's side bank (forward facing mount engine), or front bank
(transverse engine) would be bank number 2, thus the forward / upstream
sensor on that bank would be "bank 2, sensor 1," and the rearmost /
downstream sensor on that bank would be "bank 2, sensor 2."