P0409 error code

[Norseman]

I bought my 2010 R51 from a Nissan dealer a few weeks ago. It has the 2.5L YD25DDTi turbodiesel.

When I looked at it the check engine light was on and the guy said not to worry, they'll fix everything before handing it over.

Sure enough, I pick it up a week later and all seems fine. They said they had replaced the EGR pump.

Then, after <100 km,  the check engine light comes on. I plug in my ODBII reader and it says 

P0409 Powertrain Exhaust Gas Recirculation Sensor "A" Circuit 

I take it back to the dealer, they fiddle with it and tell me "the computer didn't re-learn properly after we replaced the EGR pump. Reset now, all should be fine."

No check engine light again, so far.

 

Question is, does this make sense or are they trying to hide something?