I have Mazda 5, 2014, about 40K miles
There is error code: p0421 - warm up Catalytic converter efficiency below treshold (bank1)

Engine is not vibrating, so I assume this is not a problem with spark plugs or wires.

I tried one of those OBD2 devices to get some additional info:

downstream O2 sensor (V) jumps between 0 and 0.9 and back; it drops to 0 pretty much every time I release gas pedal (while driving on a freeeway), 
	
upstream O2 sensor (Current, mA) was around 0.03 and at some point jumped to  -40, then to -127, then got back to -0.1

**Mode6** scan returned OK status for all data points except this one:

 


    Catalyst Monitor Bank 1
    Manufacturer Defined Test ID range — 
    This parameter is an identifier for the test performed within the On-Board Diagnostic Monitor.,    ,✗  
    Status: Test Fail  MID: 21 TID: 80 
    MIN: 1.4999819 
    VAL: 0.9999879 
    MAX 255.9930000

Here is some data collected while driving on a freeeway, around 60mph
[![enter image description here][1]][1]

There is a [TSB][2] pointing to similar problem but for other Mazda models, not Mazda 5, according to this TSB "*This is caused by improper control logic of the PCM that may detect false error of the A/F sensor, resulting in false detection of P0421. To correct the problem, the control logic of the PCM has been changed*"

**Questions:**
What could cause this problem? (afaik, catalytic converter is still under federal warranty ( under 80K) - could it be it, or should I try to replace O2 sensors?

What is Catalyst Monitor Bank 1? (sorry for being ignorant, I tried to google it but I still don't understand, if this is a part of computer or one of the sensors or something else)

Thank you!


  [1]: https://i.sstatic.net/SbuMB.png
  [2]: https://mazda.oemdtc.com/376/check-engine-light-on-with-dtc-p0421-2014-2016-mazda