Prospeeder

its bad cats, yet to ever see cat codes from an o2 sensor. Its using a very logical pattern to figure out over the course of many drive cycles if the converters are working correctly. Comparing them to the signals before the cats. It will see high fluctuation in mixture after the cats meaning the cats arnt working. The sensor cant magically crate more voltage and fluctuate, its not how they work. The cats are bad.

Airbag

yup those are bad cats i would think .
You can in vag com tell if they are aging O2 sensors or if the heater element is gone but those are completely different codes...

However .. if you want to try ........

if i were replacing the cats i would replace all 4 o2 sensors anyway .. in for a penny in for a pound. So if you are up to it you could repalce all 4 first and see what happens for your own peace of mind. bu i think ur gonna end up with new cats by the end ..

GTA_Driver

It is expensive (as in, more expensive), but it is a good idea to replace all O2 sensors with the cat.

aca6c5

Well, i decided to hook up my scanner again while the car was @ full operating temp and watch the live data. The live data scans and reads voltage of all O2 sensors. Being that the 2 that have been throwing the codes, bank 1 and 2. I watched those as I let the car idle and during rev's between 2500 - 4k.

Can someone tell me if these numbers sound right while is at a steady idle of 2500rpm
b1 - 0.7 - 0.1v
b2 - 0.1 - 0.08v

Now bouncing the revs between 2k - 4500, the voltage is all over the place going anywhere from 0.7 - 0.1 on bank1 and 0.7 and 0.08 on bank 2.

during idle the voltage on both banks go from 0.7 - 0.1v. From my google searching a fully functional O2 sensor should read voltage around 0.5 - 1.0v Mine never see 1v as they're bouncing around from 0.7 - 0.05v

Also to note, while revving i saw bank 2 o2 sensors go straight to 0.00v. I would think that would be bad.

I do have a video of this, but I need to get it uploaded to utube 1st.

Thanks!

Prospeeder

ok this is how an o2 sensor works. its creating a voltage signal out of the oxygen different on each end of the sensor. If the voltage is high up to .9 to 1.0 volt, than theres a big difference, or rich. If theres low voltage 0.1, theres not much difference, so lean. They will bounce back and forth rich lean rich lean and the ecu uses those signals to keep mixture proper. If the Cat is working, there should be very little fluctuation of voltage from the sensor. Thats how it knows its working. if the sensor is fluctuating like the front oxygen sensors, that means the cat is not working and it sets a DTC after so many drive cycles. By what your saying, the cats are bad. Stop wasting your time on the sensors themselves, there fine. Normal range is .1-.9 volts. 1.0 is like mega rich holy crap its just dumping fuel, obviously your not going to see that.

2.7Lturbo

but what about spurious sensor signals from a faulty component? couldn't that simulate the same readings while being an electrical issue?

although im inclined to agree that the cats are indeed the issue

Prospeeder

o2 sensors fail by getting slower and slower response untill there is no more response and it sets a no response code. Of course the heater element can fail and set a code also.

Airbag

just as a data point and not a recomendation : about a year ago i changed the cats . what a huge nightmare diy.
a year later one of the o2 sensors failed.. repeated pita. should have done the sensors. lesson learned.

Just Me

i think you have it, btu that's a pretty confusingl;y worded response.

The O2 sensor measure residual reactive oxygen to see how much is Co2 (by product of combustion). For the engineers out here, from here its a simple negative feedback loop. If the figure is too low, you have unburned HCs. Too large, its too lean. Teh mixture is adjusted accordingly.

Now, the o2 sensors are also used for a different purpose. They measure the gasses before and after the cat. If its working efficiently, the difference is large (%). If they are not, its relatively the same (%). So a small delta can means:

1. dying cat
2. higher reading from o2 sensor #2
3. low reding from 02 sensor #2
4. combination of above

Its very hard to be 100% clear.

God did it.

Grant

Juniku

I paste my answer from another topic liek this: