I'm getting code P0431bank 1 below threshold. It started out only happening about once a month, but now comes on and stays on. No affect in performance or gas mileage. I read that this is sometimes caused by a secondary air injection vacuum leak. I checked for leaks in my system and none. Do I have a bad CAT? Precat?

 

If you have a 6sp there is no SAI, it most likely a O2 starting to fail.

 

P0431 warm up catalytic converter, bank 2 - efficiency below threshold

causes are cat, wiring, HO2S 2 ( heated o2 sensor 2 )

 

OK, thanks. Which O2 sensors or sensor is failing. Do you generally replace all 4.

 

sensor will probably soon throw a code. then replace that one. (for example Oxygen (lambda) sensor B2 S1 : open or short to ground)

B=Bank
S=Sensor

 

Also if your cat is bad and your under either 80k or 100k I believe it is under warentee