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Old 04-12-2011, 08:29 AM   #8
Registered User
Join Date: Aug 2010
Location: Ogden, Utah
Posts: 207
My Ride: 1999, E46 328i
El Polo...

Its not that no one knows its more that trouble shooting emissions systems is a PITA and cant really be explained in a few posts. I'll try a fast run down of the basics.

Bank 2 sensor 2 is your back Cyl 4,5,6 post cat o2 sensor.

Look at post 38 on the link I posted.


On your graph you posted, there are a few things to be looking for one is the way the post cat o2 looks while running cold and hot 1 minute doesn't really give enough information but there are two deferent patterns for the post o2 you could look for.

Cold- you will see an isolating pattern as the voltage changes up and down the system isn't hot yet
Hot - this pattern should even out as the sensor starts reading the hot air and is giving the computer the current information.

Also sensor 2 should not flux with sensor 1 that could be an indication of the cat failing.

Sensor 1's job is to talk to the computer and tell it if its adding to much or to little fuel, Sensor 2's job is to make sure the cat is burning the rest of that fuel.
As sensor one is adjusting constantly do to the ever changing conditions of the motor the cat should burning extra fuel so that sensor 2 reads an constant emission output or fluctuates more slowly.

Sensor 1 reading should be fluctuating up and down
Sensor 2 should have a slow lightly fluctuating reading

Basically my point is if you don't know how to diagnose a o2 have a shop do it, Then replace the part yourself if your so inclined.

There is allot of information on Google about the diagnosing of these problems lucky for you every car has emissions systems so there is allot of very good information, but its better to have someone with the know how of how the system works and how other parts can effect its operation.

Thats all I have to offer :/ Hope it helped a little
GuitarmanTT is offline   Reply With Quote