Dogginator

I have a friend who recently moved to the north side of Houston (15 miles north of the beltway). They have a 2007 Volvo S40 that has a CEL for the catalyst efficiency. What are the emission requirements for TX? Also, does anyone know of a reputable Volvo mechanic in the area? Is the Volvo dealer in Houston reputable?

I told the friend that items should be replaced in the following order: primary O2 sensor, secondary O2 sensor, catalyst.

Thank.