The dealers ( although expensive re the diagnostic ) should be able to solve the fault by looking into any faults that have been logged by your vehicles computer. They will also be able to clear the faults.
The dealer also has very specific dectection conditions + fault finding procedures for
Catalytic converter fault finding
Oxygen sensor fault finding
If the diagnostic tool shows "Oxygen sensor On Board Diagnostic: done ... ACTIVE" or "Validation of the oxygen sensor repair ...1DEF", the control cycle has not been carried out correctly. In this case, the dealer must repeat the cycle of testing ensuring that the detection conditions are complied with.
If after the test, the diagnostic tool shows "Catalytic converter operating fault ... ACTIVE" or "Validation of catalytic converter repair ... 2DEF", they must refer to the fault finding method associated with this symptom.
In short the whole process takes a long time to complete if done in strict accordance with instructions.
If you have just received your P45 just before Xmas I can totally symp with you having experienced the same thing last xmas. Go work for yourself if you have skills. I can recomend these
people to look after your initial start up ( good luck )..
Stu ( L20 )