MOT emission fail, no error codes

[nicemd]

Hi,
My VW Passat 2.0 -06 failed MOT emission test the other day.

CO @2500 4.8 (0.2)
CO @idle 3.1 (0.3)
Lambda 0.88 (0.97-1.03)
HC 364 (200)

The engine is running fine and I can't say I feel any lack of power.

What puzzles me is that the engine is running rich, but I have no error codes?

Suggestions where to start looking, please?

[trickywoo]

O2 sensor problem is a common reason for numbers like that.

[nicemd]

Wouldn't a faulty O2 sensor generate an error code? Or is it possible it is "just a little bit" faulty?

[stevieturbo]

nicemd said:

Wouldn't a faulty O2 sensor generate an error code? Or is it possible it is "just a little bit" faulty?

Engines can have many faults that will not generate a light.

Lambda sensor could be the problem, simplest thing to do is test it.