emissions control unit '01 XJ

My emissions control unit is ticking....what does that mean is it shot? the check engine light is on but it the code reader says its an O2 sensor.

any help would be helpful thanks:banghead::banghead:

I don't know about the clicking....but I'd replace the O2 sensor and see what changes you have.

is this one of those units that clicks after a pre-determined amount of time..