P0135 I replaced the down stream O2 sensor and its still on i need help
2004 honda civic lx

 

have you checked all of your wires back to your ecu for continuity? if you have a charge from all of your wires thats a good step toward figuring out the problem...
the other thing you could try is if u didnt disconnect the battery before putting in your new o2 sensor then u must disconnect it again remove your positive battery terminal wait a few minutes plug the o2 sensor back in and then reconnect your positive terminal then decode you car and erase any code that may still be reading.

 

Which sensor did you replace? P0135 is for the primary o2.
Yes, resetting is required.
Also was it one that came with a plug or did you have to add the plug yourself?