Engine light ?

Get a scanner and check the trouble codes.  You are just guessing right now.

the OBD ii system only monitors electrical components. So it's not a filter. Air sensors are not in the emission system for leaks. A charcoal canister vent valve or purge valve may be your problem BUT it's cheaper to have the problem diagnosed rather than throwing parts at it with your fingers crossed.

Ideally you should get the car scanned with a high level or dealers scanner, a basic scanner probably won't do, as I found  mine was not suitable for all diesel engine.faults

I had the same message on mine and could not pin it down with my scanner so eventually I had it scanned by a specialist French car garage who found it had a short circuited glow plug and a burned out glow plug relay, I replaced all the glow plugs and the relay, regenerated the DPF, as advised, and all was OK.

The garage said they had come across this before on Citroen - Peugeot diesels. So it may be best to get your car properly scanned.and the fault codes obtained.

Hope this helps.