Has anyone had to track down a P0422 - Main Catalyst Below Threshold, Bank 1
I am wondering if the catalytic convertor has gone bad or if the O2 sensor is having problems. The front O2 sensor was replaced about 6 months ago with a Bosch Universal from Autozone but the rear O2 sensor is the Volvo original from the factory. It has 123,000 miles and has been on the road for 6.5 years. I may just replace the rear O2 sensor with a universal so see if it solves the problem, but I was just wondering if anyone else had tracked this down and what the problem ended up being. Thanks in advance for any help. - David

was there any other codes at the same time? have you checked for vacuum leaks, the intake manifold gasket maybe? i would do the simple things first.

No, that is the only code that showed up. I am using Alex's OBD-2 software on my laptop and other than that, everything seems to be fine. Of course being a shadetree mechanic, about the only thing I can look for in the displays is an error. I don't know if a lot of the information it is giving me is normal or not so I just look for some tye of errors. I did go ahead and order the rear O2 sensor and I am going to replace it as soon as it gets here. Since it's the original and with 120k+ miles, I am sure it is about time to replace it.

What is your vehicle & Year?
I know I have Alex's OBD software on laptop and it would sure be nice to learn about all the other info listed there and how to interptret it?
D~