A faulty O2 sensor would trip a check engine light.If the "emission" lamp you see looks like a muffler-esque symbol with heat lines coming off it, it is your Catayltic converter heat sensor activating. Honda's are notorious for that sensor to go bad, rust off, or the wiring to get pulled out.It is there to let you know the Cat. Converter is malfunctioning (if it is working correctly) Replacing one from the junkyard will do. (If it is that sensor) Not a good idea with o2 sensors.