O2 sensor or Catalytic Converter
 

I have been having this recurring problem for years and am having hard time believing that I have a bad CAT, I own 2004 2.5T V70

Both o2 sensors have been replaced with OEM Bosch equipment. The car drives great and get awesome gas mileage in the city, 22mpg and on the highway 28-29mpg, cruising at 70-75mph. Have had the oil bath evaporative cleaned and oil lines cleaned, including the throttle body.

I can clear the code, P0420, drive it for approximately 45days and the code appears again.

I need some addition insight, if my CAT was bad, my performance would be bad too. I'm reluctant to spend the $$$ on a new CAT thinking that this problem would re-appear.

Suggestions, this is great running vehicle with only 135k, it has plenty of life remaining.

I could be wrong but I don't believe that you would get a performance degradation from a bad cat. All you really get is more polluted air entering the atmosphere.

For what it's worth, I had been getting a cat-related CEL code regularly and noticed that it happened whenever my oil level was low. This led me to troubleshoot the oil leak which I found and addressed. CAT code has not re-appeared since....could have been a coincidence though.

I agree with you - more pollution but in my case my pollution readings haven't changed and North Carolina reads pollution every year when your car is inspected.

As for the other comment, the car doesn't use any oil - this continues to baffle me.

But the repair shops keep saying that a new CAT is needed. If I replace the CAT and the problem doesn't go away then I am out $1.2-1.5k and I am not comfortable with that repair cost.

There must be something else, but what

You could try putting an o2 sensor spacer on the exhaust sensor to see if that works. I think you can get them at IPD

Replace the cat. It is not that expensive and not that bad to change.

Checking prices, the cat for your car is about $275.00.