98 Hyundai Elantra OBD II Codes

My check engine light came on so I took the car to AutoZone and had the
codes read
P0422
P0712
his little manual said the 422 could be cat, o2 sensor or a few other
things and nothing about the 712. A google of the 712 says trans fluid
temp circuit low. the car just had a new trans put in so i am thinking
this one might be stored, is there anyway to narrrow down the 422
though?

 

First, repair any exhaust leaks. They can confuse the computer into
thinking there's a catalyst issue.

Then, to decide whether the oxygen sensors are working properly, you'll
need to look at their waveforms. The front one should cycle from low to
high voltage when hot idling at least once every three seconds. The rear
should remain relatively steady. If the amplitude of the rear oxygen
sensor waveform is similar to that of the front oxygen sensor waveform,
then you need a new catalytic converter (the one between the two sensors).