REPLACEMENT ADBLUE PUMP.
With a rated service life for the Adblue module of 24,000 hours, these pumps were never going to last forever!
The Main function of this component is to deliver AdBlue solution to the Dosing valve from the DEF tank and vice versa. It is a “positive displacement” pump driven by an electric motor. The direction of motor rotation is the same for filling and emptying of the AdBlue unit.
A deteriorating pump motor could lead to faults which are pressure related or loud adblue pump recovery noise. I usually change this component for customers and fit a seal kit which solves leaking and pressure fluctuating problems 
9 times out of 10 this procedure fixes the adblue pump issues.