CEL with P0420 code
 

What's the most likely part to replace with the P0420 code from the check engine light? Is it the pre-cat ($200 eBay) or the back cat ($200+ eBay) or the O2 sensors? My CEL has now been on for over a week and January 2010 the car is due for inspection. North Carolina inspections are a little easier on smog then CA.

Could also be a vacuum leak.
I would guess front O2 if all else is good.

Well this is a little odd. I changed the spark plugs this weekend and the light went off. Two of the plugs had worn down the metal tip that pokes out of the insulator almost all the way down to the insulator while the other two still had a sharp point sticking out of the insulator. The car had Volvo plugs in it and I replaced them with Bosch.

Yes weird.

whaa?

It was spam and it is deleted and poster was banned.

Driving into work today (only seven miles to the office) there was a very bad rotton egg smell and it wasn't coming from me. CEL is still off but the odor was so strong. Will a bad catalytic converter give off that odor?

Yes it can.

Thought so.

Well the CEL came back on again. Is it more likely for the front pre-cat to give off that odor or can it come from the back one as well. I'm just trying to figure which part to change first.

I would do the front one first.

Is it okay to use the generic O2 sensors (the ones without the connectors) since they cost about $30 as opposed to the Volvo ones that cost $130?

I think you'd have to splice the wires to make it work. I've heard of people using them before though.

Volvo's hate spliced O2 sensors.