The CODE tells you which sensor is flaky.
There is a code for each Bank 1, Sensors 1 & 2, and for each, Bank 2,
Sensors 1 & 2.
Bank 1 Sensor 1 is the bank that contains exhaust from Cylinder 1, Bank 1
Sensor 2 contains the exhaust from the other three cylinders. Bank 2,
Sensor
1 is the CAT that has processed exhaust from the pipe that contains
exhaust
from Cylinder 1, Bank 2, Sensor 2 is the CAT that contains exhaust from
the
other three cylilnders.
The CODE will tell you specifically which sensor is tossing up an error.
Give us the Code you are getting, and we can tell you which sensor is
toast.
You can extract the code(s) with a OBD II scan tool, there is no need for
any specialized BMW tools. The OBD II data ****t lives along the bottom
edge
of the dash board, either clearly visible OR hidden behind a small cover
that is clearly marked -- I believe BMW puts the ****t behind a small cover
and marks it as the data ****t. (The OBD II spec. requires the data ****t to
be easy to find, so you do not need to spend more than about 5 seconds
looking for it. Start your search near where your left leg rests while you
are driving.)
The Code for the Bank 1 sensors can be MALFUNCTION, TOO RICH, or TOO THIN,
(3 separate codes, one for each condition) or a Code related to the
failure
of a heater that lives inside of the sensor itself. I forget the Code
options for the Bank 2 sensors, but they will translate to the CAT being
ineffective. There is a chance the CAT is dead, but a far better chance
that
the sensor is bad. I have never had a CAT go bad in all my years of
driving
cars with CATs in them. That is not to say that a CAT can not fail because
they can, but it is rare and under normal cir***stances the owner/operator
of the vehicle has introduced fuel that is not suitable. (One must search
out unsutiable fuel, so the odds of this are very low and the effect is
very
rapid so you would remember the event it it occurred.)
There can be multiple codes for any sensor, so a problem can percolate
through the computer in different ways. If you have a code for Bank 1
Sensor
1 and Bank 2 Sensor 2, odds favor only one of them being bad, and the
other
re****ting an out of spec condition that comes from the first in the stream
not working right. If Bank 1 Sensor 1 mis-detects the fuel mixture, and
adjusts the Fuel Injector Timing to cause more or less fule to be
delivered,
the result can be that what flows past Bank 1 Sensor 2 is out of spec. In
this instance Bank 1 Sensor 2 is okay, and only Bank 1 Sensor 1 is giving
you trouble. If Bank 2 Sensor 1 (or Sensor 2) is throwing a fault in
isolation, then the sensors at Bank 1, Sensor 1 and 2 are working okay and
do not need attention.
Basically, replace the sensor closest to the engine (as the exhaust flows)
first to see if it resolves a false re****t from the next sensor
downstream.
If the downstream sensor is throwing a code, but the upstream sensor is
not,
then do not replace the upstream sensor.
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