VQ35DE simultaneously throwing P0420 and P0430 codes - flex section leak?
 

Got both bank codes on the way home last night after driving for about 20 miles on the HW.
Cleared the codes, and they did not re-occur this morning on the way to work.
Does this normally mean that the flex section rotted if both are thrown simultaneously?

Are our engines known for throwing cat codes due to a bad PCV valve? I'll prolly try to replace it just in case anyway.

No, not necessarily.

P0420 code simply indicates that the voltage from the rear O2 sensor (i.e., the sensor after pre-cat) is not as "flat" as it should be. P0430 is provides the same information from the other bank.

To explain: Normally, the voltage from the front O2 sensor follows a sinusoidal wave, and the voltage form the rear sensor is flat. This difference indicates that most COx/NOx byproducts have been eliminated by the converter. Codes P0420/P0430 indicate that the voltage from the rear O2 sensor is not flat (and perhaps is sinusoidal, just like that from the primary O2 sensor) - hence the conclusion is that the pre-cat in not performing its function.

So, I am afraid that: Your codes simply indicate that both of your pre-cats are worn out. Given the age of our cars, this should not be unexpected .... .
Note: It is also possible that your O2 sensors are bad, and that they are giving you a false signal. Possible, but not very likely (guess how I know).

How can you tell your precat is bad/going out? I have a catman Y, so the back is deleted. I'm kinda worried the front may be beginning to fail at 170k miles.