Engine management light on after fitting decat

[elmo2002]

I fitted a de cat to my 172 cup yesterday but noticed when i was fitting it that the second lamba sensor hole was blanked off so although the sensor would screw in it wasnt in the exhaust flow. I took it out for a drive and all was fine. Then when i took it out last night the engine management light has come on but the performance doesnt seem to have been effected.

How can i turn this light off and keep it off?

 

[DrR]

It's telling you your cat is broke.

 

[elmo2002]

It's telling you your cat is broke.

I've shown the car that the cat isnt broke its just not fitted lol. is there no way to turn the light off?

 

[Homer-Simpson]

Surely it is the emissions light and not the engine management light? :S

Also if you haven't fitted it then it will come on, the sensor sits there reading values about X. It has a lower limit and an upper limit, if either of these are hit then it will turn the light on (or that is the way I see it).