my 2004 wrx failed its mot today due to emissions, the mot tester said that my car was producing to much carbon monoxide, the co2 levels were fine and the lamda readings were all ok. the cat and lamda sensor are barely a year old so i am struggling to find any reason as to why it failed.
my car has been remapped is is running 340 BHP i only use shell optimax and i also use a high octane fuel additive, could this be affecting the reading? i am struggling to find a reason why it failed any help would be appreciated, thanks in advance.

 

Did he test it when the engine was hot? If the egnine was cold you usually get worse readings and retesting it when hot can see it pass.

 

What was the HC?

Blind guess; You have a misfire, or the catalyst wasn't warm enough (especially if its a sports cat as these have less substrate - car needs thrash immediately before testing).

 

Yer as has already been said, my local dealer on a standard WR1 needed to run the car on the ramps at 3k rpm for 10 mins to get the exhaust system hot enough to pass it without any mods. A cold emisions test would definitely fail MOT.