Looking at this for failed mot emissions, garage have replaces the NOX sensor after nox heater fault code and no activity on nox live data, I've updated the ecm to the latest software which is required after replacing the nox sensor, checking the nox reading after the update also shows it doing nothing and the voltage static at 0.16.
Gone through all the wiring to the nox ecu and everything checks out ok. Can someone advise what live readings i should be getting on the diag tool for the nox.

These were always hard to test, they never really took off and didn't stay fitted for long.

I wouldn't get too hung up at looking for a reading, nitrogen oxides are formed at very high combustion temperatures, usually at high loads with levels of detonation. You're not going to really going to get any usable data in the workshop, a static voltage would probably be correct, they also have a specific type of cat fitted to this model too. I would be looking elsewhere for an emission fault.

Apologies in advance if I have this wrong, but it's always been my understanding.

What fault codes and emission data are you getting?

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.

Steve
As Chris has mentioned NOX Cat and NOx sensor will have no effect on MOT emissions, as you know they don't measure NOx, look upstream for your problem--possible inlet valve coking??

Many thanks guys for your help, i blame myself on this one for not doing my homework!..they took it for a retest today and it sailed through so not sure how or what I've cured, only thing that might have helped perhaps was the ecm update.