DPF pressure sensor clarification

[belgarboy]

Hi, recently did a forced dpf regen as the check engine light came on and Forscan stated the efficiency was below the threshold. I'm trying to check if there is an underlying issue and am starting with the differential pressure sensor. However it has just one input. Guessing it compares the dpf pressure with barometric? Does anyone know what the PID code is that I should be looking at? The delta pressure sensor reading is zero. If this really is the differential pressure then it needs replacing, it just doesn't look it with it's single input. Can anyone clarify for me? Many thanks