P0135 Heater Circuit Help! PLEASE!

allright listen. i know a good amount about my accord. i have a 1999 honda accord lx. im on my 2nd motor which is the ulev motor and 3rd tranny which i recently just conversted from A/T to M/T. ok. now. i have one lkast code left onmy car everything else is good.

its p0135 primary 02 sensor heater circuit malfunction.

-i replaced the sensors with honda denso parts from dealer. made for my ulev motor.

-i checked the fuse and relay which both are good.

-i checked continuity under the hood to pin 4 which is the white wire under the hood.

i cant figure it out any help at all would be great thanks

In my codes library it just says an O2 sensor. Is there any reason you decided that this was a primary?
I would probe the secondary (after catalytic converter) one. If it proves to be good I guess you need to check the ECU pin outs, according to the electrical diagram, which I unfortunately do not have.

Good luck,

Sam