Hello

if the car drives OK with the light on then its likely to be something minor

On any car if you get a check engine light or other fault light this typically means one or more of the sensors has failed or has a faulty connection.

The ECU senses this and may put the car into 'limp home' mode which typically limits the revs and the amount of power available. Usually the car is safe to drive for a short distance as the mode is intended is intended to get you home without incurring any engine damage

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

You can do a very rough and ready check yourself by unplugging sensors one at a time and seeing if any of them change the driving condition which would indicate the most recently unplugged sensor is the faulty one. This method is not foolproof though and reading a fault code off is the better method.

it may also be an issue with the Diesel Particulate Filter ( DPF)
if the ECU thinks the DPF is blocked then it won't allow full engine power so I'd suggest;

taking the car for a long drive where you can keep the engine rpm up over 2000 rpm fro around 30 mins this will get plenty of heat into the system and get the system into re-gen mode