My 2011 6.6 LML has another check engine light; this time the code is a P205B translated to a "Reductant Injection Air Pump Circuit Open." Can anyone provide some insight on what this means and how I can fix it? I'm tryin to avoid my local dealor, I think they just like seeing me come back every couple of months! ANY help is always appreciated!

 

The DTC description you gave does not match the code you posted
P205B Means "reductant tank temperature sensor performance" as per GM shop manual.
The PCM is seeing a reported reductant tank temperature out of range from this sensor located in the reductant tank. Without a tech 2 or equivalent to see what the sensor temp is reporting to the pcm theres nothing you can do in your driveway to alleviate it. IMHO time to take it back to the dealer and let them look into it.

It's a new diesel check engine means return to dealer and bend over they aren't designed to be tinkered with by the DIY'er anymore unfortunately.

 

That is the sad truth of todays vehicles, especially the new breed of diesels. As even an 02 DMAX is too complicated for the average mechanic.