Hello
After several months and lots of help from this forum (Thank you), I have gotten my 2008 Vue to run, and have only one CEL code.
P0422
I am about to take it to a mechanic to have them troubleshoot the issue, but thought I would check-in for anything I can look for first.
I have a scan tool have been able to monitor some readings. I can customize what to view, but I'm not sure what I should be looking for.
If someone can give me some direction, I will see if I can narrow it down. Or if you think I should just take it to someone, I'm about done messing with this, so I won't argue...

 

P0422 is very similar to P0420, and indicates your catalytic converter is going bad. See https://www.obd-codes.com/p0422. You'll note that changing O2 sensors will not correct the problem. In fact, only because both O2 sensors (on a given converter) are working properly can this code be generated.

If it is confirmed that your cat is bad, BEFORE YOU REPLACE IT, find out what made it go bad, and correct that problem. Look for excessively rich running (or extremely lean running, cooking the catalytic elements), contamination with oil or coolant, damage to the converter or the exhaust system near the converter, etc. I don't know about the Vue, or other Saturns, but some cars are very picky about what type replacement cats are installed. Cheap out, and you may run into the same problem much sooner than expected.

 

You said you had a scanner that can monitor live data. Watch the B1S1 (or B2S1 if you have 4 O2 sensors), and you will see the numbers varying between about 0.1 to 0.8 or so. Now watch the B1S2 numbers. They should vary very little between about 0.5 to 0.7 or so. This is because the catalyst elements are using the excess oxygen in the exhaust stream to 'neutralize' carbon monoxide and nitrous oxides, etc. If the B1S2 numbers are changing similar to the B1S1 numbers, it's an indication that the catalyst elements are no longer absorbing the excess oxygen and doing their job.

 

I just went back and read through all of the posts under your thread titled p0172. I know that you replaced O2 sensors. Did you replace both before and after the cat with denso's or did you replace only the upstream one?

I asked because I have seen with my own eyes and my own vehicles a p0420 catalyst below efficiency threshold code pop up. Looking at the data of both O2 sensors as a function of time is critical.

However, I have replaced the rear O2 sensor on both of my SC2 vehicles and completely eradicated the catalyst code. It was something a Saturn tech taught me which was that as your catalyst gets exposed to more and more exhaust, so does the rear O2 sensor. As the cat gets near the end of its life, you start to get deposits on the rear O2 sensor which impair it's ability to function properly.

Remember that this code is based on a mathematical calculation of the real-time response and voltage levels of each of the front and back O2 sensors. If something blew in the old engine and it's sprayed a bunch of oil and other crap into the exhaust, both the converter and the O2 sensor May be trash. However, it may be that the road to sensor is poisoned and the voltage going into the calculation engine above a falsely triggers the code.

I'm not going to tell you that you should go replace the O2 sensor in the rear period all I can tell you is from experience and factoring in the age and mileage involved, it is possible that you may not need a new cat for a while longer. But to lbrainer's point, if there is something else that is being improperly fed into the exhaust stream, that needs to be addressed first or you will simply trash a new cat or a new O2 sensor.

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