Are you struggling with limp mode and a recurring P2456 code on your 2015 TDI?  

This issue is typically caused by a failing differential pressure sensor assembly under the head shield located near the fire wall. Opening the heat shield normally reveals a melted assembly.

The sensor assembly is made up of two differential pressure sensors. The sensors can be changed individually in the assembly but when the items are melted it is always suggested to replace the entire assembly:

The sensors measure the backpressure from the exhaust and tell the vehicle’s ECU when a regen should begin to clear the DPF of soot. When the sensors begin to fail the car will go into limp mode making it lose power. If the sensor is cracked or damaged it will leak hot exhaust gasses causing the plastic sensor assemblies to melt. 

Why are the sensors failing? The most common cause of failure to the sensor is after a timing belt service. The hard vacuum lines from the DPF to the sensor run across the timing belt cover.

When moving the lines to access the timing cover the plastic sensors often end up cracked causing a leak of the exhaust gasses. These small cracks will lead to the start of the issues with limp mode occurring first followed by the CEL and then the melting of the assembly. The codes from the check engine light could be any of the following which are related to the DPF Sensor A: P2456, P2453, P0641, and P2454.

To avoid this issue we suggest removing the sensors first when changing the timing belt to avoid damaging them when removing the timing cover. While you have the sensors removed they should be inspected for damage and replaced if necessary.