SMAX Diesel Particulate Filter Issue

That sounds like a plausible diagnosis. Reduced power and smoke often point to DPF problems. Have you checked for any error codes using an OBD2 scanner? Low exhaust pressure could indeed be the sensor, but it might also be a blockage somewhere in the exhaust system. Has the car had any recent exhaust work?

I haven't checked the error codes myself. I was hoping to get some opinions before taking it to a mechanic. You mentioned a blockage – where would that typically occur in the exhaust system?

Without the error codes, it's tough to pinpoint the exact location. Blockages can happen in the DPF itself, or even further upstream. Considering the symptoms and mileage, the exhaust back pressure sensor is still a likely culprit, but a proper diagnostic at a workshop is really the best way forward. You don't want to risk further damage.

Thanks for the advice. I took it to a workshop, and you were right. It was the exhaust back pressure sensor. Repair cost was 245€. All sorted now!