Common reasons why a 2002 Jaguar S Type 3.0 fails passing a smog test?

There are many things that can cause an emissions failure, it is important to know what readings were out of spec when it failed. High CO can be caused by faulty MAF sensor, leaking injectors, faulty pressure regulator or bad converter. High HC can be caused by dirty injectors, faulty ignition coils, faulty spark plugs, faulty cam timing solenoids/actuators or bad converter. High NOx can be caused by faulty EGR system (if equipped), engine overheating (or running hotter than normal), faulty cam timing solenoids/actuators or bad converter.