Garage cleared all the fault codes but i was told one of them was for the nox heater, I will try and find out from them what other codes they had and emission failure figures. They also replaced the nox cat at the same time but that was probably a pattern part, they could only get the nox sensor from dealers at about £400 Because of not seeing any nox activity after the ecm update I was thinking there might be a wiring problem, now it sounds like i should have done my homework on nox sensor expected diag readings, as i spoke to ALogic about this static reading which on the old nox was 0.80v and the new one is 0.16v and they suggested there might be a wiring issue, they didn't mention that the reading is probably ok and will only start working under load. Seems like i might have put the cat amongst the pigeons now telling the garage the new nox isn't showing any data changes and might be a faulty new part.