Fit a decat and see if your EML even comes on, it may already be disabled in your current map file.
If it comes on, get the mapper to map it out so you dont get EML.
If your map is to suit a car with a cat in place, then you remove cat and only have map tweaked to rid the EML, then you put cat back on for MOT- you can still drive it hard as it was mapped with a cat anyway.
Only time you couldnt drive it hard with cat fitted is if its been mapped without one (and itll have smaller downpipe than a decat).
The rear lambda which you get mapped out is not important, its there to make sure the cat is doing its job, hence why it pops a EML when you remove cat. The front lambda is the one controlling the fuelling.
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