Error code p21dd

[rcmike]

Check engine light came on and local parts store says it read code p21dd. It a 16 Silverado 3500 with a duramax. Runs good still but was thinking it may be something simple before it goes to dealer.  Thanks for any help in advance 

[mjm-1957]

Reductant heater1 circuit low. Depending on how many miles you have might be covered.

[1st diesel truck]

 

[rcmike]

I did a search on you tube and saw what it was . I took it to dealer for also a oil change and it was covered under warranty so I was relieved. The bill would of been about $500 but he said that the def stuff was still covered under my warranty. I got 43k on the truck.   Thanks for the response .