Do I need auto electrician or mechanic?

[Scottoiii]

Hi. I have a 2013, 3008 diesel automatic. Hope someone can help. My car runs fine the first time I run the engine, no problems. Then, if I turn the engine off and start it again with 10-15 mins the engine fault light comes on and usually stays on, with the car in limp mode and loss of automatic gear changes. A friend (mechanic) ran an obd check and this showed it to be the engine additive tank underneath (that I had no idea existed). Will this be a short or is the tank/motor knackered, or is it just out of additive? Don't want to be shelling out unnecessarily as need to decide whether to re MOT and keep or sell. Ordinarily I'd swap the car but trying to wait the car price hike out. Any help appreciated

[deccadick]

Is it needing Adblue replenishment?

[telmel]

It could be a DPF bag that needs replacing
Mine burst and was dripping the black solution, my mechanic removed it and fitted a new bag, cost 220 euros plus fitting , who knows what peugeot charge ?