De-catting and new MOT rules

[Ruan]

You can't check the Cat on a diesel for how well it's working unless you were to put it on a dyno and get the engine up to proper operating temperature and then cruise for a while and measure the NOx and HC output - which they can't do.... Any other time it's not operating properly as it's not under enough load, you might get a bit of NOx on idle, but generally the combustion temperature is nowhere near high enough to cause NOx to be produced...

And as of yet, there's pretty much NO reliable way of measuring NOx content in exhaust gasses...