2006 Hyundai Elantra - P0136 code

What can cause a bank 1 sensor 2 to read a 1.0 in voltage? Check engine light is on, I replaced the sensirs and deleted the code several times, it comes back on very quickly. Any ideas?

Did you replace it with an OEM? There could be other problems associated with that CEL code.
1)Harness is open or shorted . 2) Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection. 3)Inappropriate fuel pressure .4) Faulty fuel injectors Intake air leaks may be faulty. 5) Exhaust gas leaks

Are you sure you installed the correct oxygen sensor?

On your vehicle the upstream and downstream O2 sensors are different.

https://www.rockauto.com/en/catalog/hyundai,2006,elantra,2.0l+l4,1432767,exhaust+&+emission,oxygen+(o2)+sensor,5132

And by the way, there’s no such thing as an OEM O2 sensor.

Vehicle manufacturers don’t make their O2 sensors. They purchase them from a supplier such as Bosch.

Tester

If the engine otherwise seems to be running ok, and that’s the only diagnostic code stored, my guess is the cat needs replacing. Good idea before going that route to check for obvious problems as posted above, especially for any engine or exhaust air leaks, the fuel pressure is correct, and a careful inspection of the wiring harness to that sensor. That sensor (along with its companion in front of the cat) compares the exhaust gas coming out of the cat to the exhaust gas going into the cat. The code occurs when it doesn’t respond in the manner it should were the cat were working properly. A mechanic that specializes on hyundai will have a specialized scan tool with functionality that allows a more comprehensive test of the cat and the sensors.