My 2019 308 Petrol 3 cylinder has had, for a while now, the 'P040 Catalyst below efficiency error'. My garage (independant) has changed the o2 sensor but the error returns after about 50 miles. He has checked the wiring etc but says everything looks ok. He now thinks it could be a problem with the catalyst itself. The car itself seems to be running well and if it wasn't for the engine warning light I would not know there was a problem. It first started after driving through standing water after some really heavy rain storms. This may just be a coincidence though. Has anyone had this issue and if so how was it resolved?
