P2459 Indicates DPF which is the diesel particle filter, usually cars that have done about 70k miles start to have this issue, if the car is only used for short runs it usually happens sooner. Sometimes the car will go into limp mode and wont go over 40MPH, The red light also usually comes on as well sometimes flashing. The cost of a replacement at a dealer is usually around £400-£500. If you buy a DPF from a motor factor it will usually be around £220 + VAT, that is what I paid for the last one. You must make sure it is "type approved" as the other ones are illegal. They are very fiddly to fit as the heat shield is awkward to remove but should take about an hour and a half to fit. Lastly you may have to get somebody to do a regeneration programme on it but you need specific diagnostic equipment for this job. Hope this helps