Skoda Roomster diesel engine issue

Low DPF exhaust pressure on a diesel can be tricky. Have you noticed any changes in fuel consumption? Also, when did the DPF regeneration cycle last complete successfully? If the sensor is faulty, it might be sending incorrect data to the engine control unit, which then affects the fuel mixture and combustion process. That could explain the smoke and smell. Is the engine misfiring?

Fuel consumption seems normal. How would I know when the DPF regeneration cycle completed? Is there a way to check that without special equipment?

If fuel consumption is normal, a faulty sensor is even more plausible, as it's unlikely the DPF itself is completely blocked. Unfortunately, without diagnostic tools, it's difficult to confirm DPF regeneration status. Considering the symptoms and your suspicion, a defective exhaust back pressure sensor seems like the most likely culprit. I'd advise taking it to a workshop for diagnosis to confirm and replace the sensor. Ignoring it could damage other components in the exhaust system and emission control.

It was the exhaust back pressure sensor. I had it replaced, and the warning light is gone. Engine power is back to normal, and there's no more smoke. The workshop charged me 245€.