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I am desperate for any assistance that can be provided for our situation. 


We are US military stationed in Germany. Our 2015 Sierra recently threw the p21dd code. We ordered the replacement reductant tank and installed it ourselves. The engine codes were cleared but we are still getting limitations on our speed and distance. We are stuck at 88kph/80km until we drop down to 6kph. In the research that I've done so far, it seems we need a manual regen done on the truck in order for the limitations to go away. 


This is where we are having the biggest issue. GM will not assist us in any way because we do not reside in the US. They constantly revert us back to the German GM entity and I've lost all hope in trying to communicate with them. We have been hung up on more times than I can count because we do not speak German. So, is there any hope for fixing our vehicle before it goes limp? If we can't get it fixed, we don't know what we will do as we cannot sell it in this state, we can't ship it in this state, and we definitely can't drive it. 


We are struggling to find a light at the end of this tunnel and would greatly appreciate any help available. 

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First off, thank you for your service. 


There's the possibility that this tank heater will not work until the BCM is programmed for the new part. GM loves doing this - big cash cow for them - pay for labor, pay for programming, so you pay twice.  For example, if the Fuel System Control Module on my '07 Silverado fails, and I replace it, the truck will not start or run until the computer is reflashed. 


There's also the possibility you got a bad, new part - seems to be par for the course these days. My experience with diesels is pretty slim, but my dealing with parts that are bad right out of the box is extensive. As a last resort, if there is any way to return the new tank, I would, and try another. Hate to recommend winging parts at it, but whenever a new part doesn't fix something, the new part is always suspect these days, unfortunately.

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