swsc - Here is a graphic of your DPF:
The Exhaust Pressure Sensor 1 G450, functions to generate a signal related to the differential pressure which exists internally in your DPF. I don't know if this signal. In order to clear your DPF of trapped carbon the engine management system executes changes in fuel flow, injection timing and air flow in order to elevate internal temperatures in your DPF to burn away trapped carbon. The "narrative" VW technician training instructions say the following about active regeneration.
Active Regeneration Function
The soot load of the particulate filter is calculated by two pre-programmed load models in the Engine Control Module (ECM) J623.
One of the load models is determined from the driving profile of the user and the signals from the exhaust gas temperature sensors and Heated Oxygen Sensor (HO2S) G39.
Another soot load model is the flow resistance of the particulate filter. It is calculated from the signals of Exhaust Pressure Sensor 1 G450, Exhaust Gas Temperature (EGT) Sensor 3 G495, and Mass Air Flow (MAF) Sensor G70.
You have a code which suggests the output signal of sensor G450 is too low. I do not know if this signal rises with rising differential pressure or falls with rising DP. This is purely a function of component and control design. It would make sense that sensor failure would output a low signal which could be error trapped by the control system. My guess is that you are either looking at sensor failure or problems elsewhere in your back end treatment system.
One of the know issues with these cars is a sticking exhaust throttle valve. If this were the case the differential pressure across the DPF would fall because your engine exhaust flow would be choked off. I'm not sure where VW draws the line, but at 77,000 miles, it's fair to argue that this is an emissions problem that may have cover under the emission warranty.
Worth asking the dealer and potentially opening a case with VoA. Call VoA and ask them if you will get warranty coverage as an emission system problem. If you are seeing a fall off in MPG or engine performance, it is likely more than just a sensor failure. In any event, if a high signal is required to trigger this one of these active regen programs and your signal is low, you are losing one of the protective triggers which preserves your DPF. This is a situation that cannot be ignored.
I continue to believe that many of the DPF issues with these cars occurs because of un-detected sensor calibration drift. In your case an error it trapped, I'm not sure that a drift in MAF output is trapped. For sure a drift in MAF could put the engine on track for sub-stoic combustion which could negatively impact DPF life.
