No catalytic converter will be needed. If your Dodge 2500 diesel was not equipped with a CAT at the factory, a CAT will not be needed in order to smog check it in California. Just make sure the engine has not been modified in any way. The way it was equipped (emissions) at the factory is the way it should be tested in California. Engine repairs, obviously, are acceptable; just no engine modifications... ie. ECU upgrades, headers, so on...
