Hello all,

I have a '99 A6 2.8 qt with 162k miles. I have recently replaced the catalytic converters with 50 state legal aftermarket units, I opted not to replace the O2 sensors because I had no O2 codes. The p0422 and p0432 (catalyst below threshold) codes have returned. The O2 sensors are original to the car but I have never had an O2 specific code. The only drivability issues I have is smoke in the exhaust and rough idle, after long deceleration.

I used vag com to measure the O2 sensor's activity, see photo attached.

Active control on sensor 2 on both banks is not fulfilled.

Does this mean that the O2 sensors are not working properly? Could this explain my catalytic converter codes? If so why is there no OBD code for the O2 sensors?

Finally is sensor 2 the one downstream of the catalytic converter?

I have had this car for nearly 10 years but I am a relative newbie to vag-com so I apologize for any basic questions.

Thanks for your help.

 

Yes.. Sensor 1 is the before cat O2 sensor and 2 is the after cat sensor. If the number 2 sensor is reading the same (or not reading at all) O2 concentrations, it will think that cat convertor is not doing its job and needs to be replaced. I'd start by replacing the number 2 O2 sensors one at a time.

 

Ok, thanks. I'll try that, update to come...

 

Be sure to clear the codes and reset the ECU each time.