Hyundai: Oxygen sensor

I have a Hyundai Sonata 2000 had fail Nox emission (Gross Polutted).
The car has no Check Engine Light on. But I found there was 2 DTCs
Code from OBDII that were
P0134 Oxygen sensor circuit No Activity.
P0154 Oxygen sensor circuit No Activity.

I looked up under Hyundai Diagostic book and it said (Check for
Contaminated or crossion). I did replaced both upstream Oxegen sensor
before CAT, and the code are still there.

I even check the voltage from the oxygen connector, but did not get
anything.

Do you have any ideas how to fix it?.


Bao

I had the same problem. In fact I have had 5 oxygen sensors replaced on my
2000 Sonata, including those with the recall. By the way, looking at the
Consumer Reports for this model, electrical is not a strong point, especially
power equipment--I have had all 4 window motors go out as well as the power
mirrors. I have a few more months before I am paid off, and wonder if I should
stick with Sonata or move up to a larger model. Anyone have a suggestion?

Thanks,

Steve