hey guys i recently failed my emissions test and this code came up P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1) now i know its because of my header that i installed and i do have a aftermarket magnaflow highflow cat and custom exhaust , and a roadrace header , and my ses light wasent working and i changed the bulb for that i was told that can throw off the sensor and i changed my o2 sensor and my ses light came back on my mechanic dosent know whatelse to do so i can pass emissions? any suggestions on what is wrong and why i cant clear this code???