My 3.2 Sport has failed its MOT with CO emissions which are way to high. Cats are in place OK.

Garage is going to check for errors etc tomorrow. But what could have caused this? Apparently last MOT it showed nearly Zero HC and CO.

 

The same thing happened to me a few years ago. Sounds to me as though your O2 sensors have failed and it has dropped back to a rich default mapping.

 

Would that result in a fault code? Can't see any faults on OBD

 

To be honest, I can't remember, but I would have thought that it would because the heater circuit on the sensor would go open circuit, but there will knowledgeable folk on here who know far more about it than me.

 

If you can run a live scan (something like Torque Pro or the likes), you will normally see the O2 sensors working, both the upstream and the downstream ones.

Their voltage is changing constantly related to the engine load and the consequent changes in emissions.
If they are broken, they will remain at a constant voltage.

Also check your MAF sensor functioning, a broken MAF will also send the ECU into default mode.

 

O2 sensor failure doesn't always throw a code. I had the same problem with my xjr a couple of years ago and the failed sensor could only be seen through the fuel trims. Have a look at my previous thread to see how to test it.