
Isn't it easier to get it fixed...
One is PRE cat so will be before the cat the other is POST cat, so after the cat. If you follow the link i provided above you will get an exact answer about how to fix it for good.
It's all very well driving around with the EM light on, but if you pick uo another fault, you won't know as you will assume the light is for the exhaust. Also the ECU may adjust setting to make the car run smoothly but reducing power/efficency.
If your going to go to the bother of getting it fitted, you just as well do the job properly IMO

Sam