On Board Diagnostic Light Up

[s25yme]

Hi looking for some advice and peace of mind. I have recently got fitted a full 3" exhaust system and uprated fuel pump. Giving it a bit of a push on Friday night up the A1 the OBD on board diagnostic light come on and stayed on. When looking at manual this comes on due to emissions levels being higher than normal. Is this correct? The car is a 56 plate wrx. The only sign that something was wrong apart from the light was that when pushing it felt like the fuel had been cut for split second then the obd light come on. I not got a "scooby" about the mechanical side of cars so any comments be gratefully appreciated. I will probably take the car to eaglesham garage for them to have a look but not sure how they will react to the exhaust and fuel pump. Does my ecu need to be reprogrammed to suit the new exhaust? Thanks Stuart