its possible it could pass. i guess its the primary one since u said its bc u changed ur header. theyre gonna use a sniffer so the fact u dont have an o2 sensor wont make a difference but about like 8 times every ten seconds it makes the computer make the car run rich then lean and switches back and forth. depending on how it is now wired up it could make the car run rich or lean and make it fail emissions. that primary o2 sensor is what really what tells the computer wahts going on and the second one behind the cat pretty much tells the computer if the cat is good. (im guessin a honda so only 2 sensors) so technically it is possible but its also very possible ull fail or u could be running ur car very lean and end up heating up ur pistons and blowing ur motor anyway lol