You shouldn't need to have anything relaced. The tractor needs a Regen cycle. The tractor will not regen if the cel light is on. This means the tractor had been ready to go into auto-regen, but auto-regen was cancelled twice. Auto-Regen will be cacelled if the tractor rpm's drops below 1700rpm any time auto regen is asked for. Sometimes you can start the tractor cold, have no cel light and get the tractor to do a manual regen. Start the tractor at idle, set the parking brake, and push and hold the regen button for 3 seconds. If you see the "regen in process" light on the dash, you have a good chance the regen process will complete. Manual regen takes about 43 minutes. If it won't complete the regen, call your dealer. He has a way to force the regen and get the tractor back to a clean condition.
In the future, make sure you ALWAYS operate the tractor above 1800rpm. If the tractor wants to do an automatic regen, it needs two paramemters:
1800 engine rpm
exhaust manifold heat
If it sees these 2 conditions are satisfied, it will go into auto-regen on it's own and complete the regen cycle. The only thing you really notice in the regen-in-process light on the dash. Auto regen generally takes less than 10 minutes. But...if the engine rpms drop below 1700 during the process, it will cancel the regen. The tractor will allow 2 "cancels", then throw the cel light and reduced power.
Best way to operate the tractor is at 1800rpm or above all the time. The tractor will take care of itself and you should never need to do a manual regen.
Hope this helps.