O2 sensor wiring harness/connector problem?

Hello, I recently purchased the vehicle listed above, the day after I brought it home the check engine light came on with p0051 and p0052. I identified the correct sensor upstream bank 2 and replaced the original with a Denso 234-9029 (like an idiot I did not test the old sensor first), to my surprise the codes returned after I cleared them. So I've been investigating further, the fuses are fine, I could not identify any frayed wires, but I did check the voltage in the harness which mates with my 02 sensor and for some reason it is only supplying 8 volts, which makes me think there is some issue in the wiring, I couldn't see any exposed wiring, and obviously would like to avoid unraveling the entire harness from the computer, has anybody encountered this problem before? Any tips would be greatly appreciated. Thanks!