the emission system service requirement light went on in my car along with the check engine light, before I go to my dealer can someone give me info as to what may be causing it. Can my mechanic do a routine check or should I go to volvo?

thanks for any help.

You probably have a bad throttle body or a bad o2 sensor.

Thanks Tech, I took it to my mechanic & he ran a diagnostic on it, came up code P04020, which is catalytic below threshold. He said it's either the catalytic (which is still warrantied) or a bad O2 sensor. Volo said it would be abot 300 to replace the sensor. Does that sound reasonable?

Sounds pretty close but I would replace both sensors because when 1 goes bad the other usually does to.

Tech, looks like this is a common problem with the S60. So can this be done by a regular mechanic other than the volvo workshops?

Pretty much anyone that can work on a car can replace the O2 sensors.Its really not that hard.