Mitsubishi Montero 2001 OBDII Code P0431

Changed all 4 O2 sensors (generic Bosh), still get the same P0431 after resetting codes and 2 days of driving, engine light comes back on, also I get the code twice, code 1 is P0431 and code 2 is P0431, what else can I do??????

exhaust does not smell like rotten eggs and I dont think there is an exhaust leak, vehicle has 116k miles and have never been seviced

Any info would be welcome. Thanks.

I too have a 2001 Montero Sport with the 3.5L engine and 120k miles. it is giving the exact same problem as you stated. 2 codes both being P0431. someone told me that the catalytic converter must be bad. i haven't been concerned with the problem until lately because i am planning on selling the vehicle. i would be interested to know if it is indeed the cat that is causing this code to continuously show up. for me, it used to come back about 2 or 3 days after erasing the codes, now it comes back after about 20 minutes of driving

what are the rear 02 sesnors doing? That will determine whether the cat is bad or the sensor