Torque app failed test: P0420 Catalyst Monitor Bank 1

[VBstephanie]

In March I had my catalytic converter and both oxygen sensors replaced. Last week (June) my check engine light came back on. I got one of those wifi OBDII plug-ins and ran tests via the Torque App after clearing the CEL. After driving around for a while all tests were OK, then suddenly one switched to fail--Catalyst Monitor Bank 1 (MID:$21 TID:$a0). Minimum test value is .35, but Current value was registered at .324. What does this mean? What should I do to fix it?

[EAD15]

What was the code that was set in the computer?

[VBstephanie]

P0420 is the code that pops, but I replaced the cat and sensors... no problem until 3 months after.

[petrified.rabbit]

That code is triggered by your secondary o2 sensor. It doesn't always mean the cat is clogged every time, it could be a faulty sensor.

The issue I have, it that you replaced it already. Did you ever figure out why the cat clogged in the first place? Was it actually clogged when it came out? these might be questions you do not know the answers to.

Currently I assume the car drives fine? The secondary o2 does not effect driving that much. Am I correct? Or Is it sluggish, lack of response, not running?

If the car runs good, and your only code is the p0420, then replace the secondary o2. Often aftermarket ones are junk, it might still be under parts warranty with only 3 month use. I only buy an o2 that has the OEM style plug. If your car is running correctly, there is no hurry. Buy it off rock auto, get the o2 tool for $7 and do it yourself.

It should make the problem go away.

If the car is not running well, or the code comes back. You need to check the cat again. More importantly, you need to know what wrong with the car that the cat is clogging. Easiest reason is too much fuel entering the exhaust because of a misfire or a stuck injector. But they can also clog easily if you use fuel additives, or have the engine cleaned (seafoam for instance). Have you had either of these issues you know about?

[TurboElk]

Unless my memory fails me I think I read (on here) somewhere, somebody had a bad injector that was replaced to fix the dreaded p0420... might be worth looking into if the cats not pluged.
I've seen cats pluged on 3 different occasions and all 3 times the vehicle drastically lost power and the exhaust was extremely hot when under load and it got horrible gas mileage.