This girl i know took off her dc sports header and the sensor was stuck in it, so she just cut the wires and installed a stock header on her civic coupe dx. she connected the cut o2 wires on to the stock header o2 sensor she started her car and got a check engine light.... I thinkshe connected the wires back up right. A bad o2 sensor can cause this to right... The two grounds were never marked different from each other she might of hooked them up wrong. could that cause it eather.