- Buick Ownership
My lacrosse has about 107,000 miles. I had no problems until a month after I had my spark plugs changed. I would get code P0420 I reset it and it wouldn't come on until about 600 miles later this happened twice. So in between the first and the last time i used cataclean to see if that would work. Like I said the light came on for code P0420 about 600 miles later. Now day before yesterday the code came on so i reset it. And today it came on with code P0420, P0430. Im wondering is it the Cat, 02 sensors, NGK spark plugs that were installed, Leak in the intake gasket when installing the spark plugs. Any suggestions???