Code P21DD (Reductant Tank Heater)

[TinkeringFox]

My 2016 Sierra 2500HD has 176,000 miles on it already and recently started eating parts. The latest part to fail was the reductant tank heater (DEF Heater). Upon cold start the check engine light came on with code P21DD. After a little reading I learned that this can result in “Limp Mode”. I was in the middle of nowhere in Northern Wyoming. Not cool! I drove down to Denver and replaced it that week. I shot this video of the repair.....

 

[avalonandl]

It would only result in LIMP mode if the main tank heater failed.

[Rodney Chambers]

I ordered a replacement,but it doesn't look anything like the original.part no.84545446 3. 120 how can this work??

[jjwest64]

My 2016 3500HD def tank heater just failed at 40k! I was considering doing the repair myself, but with a time limit before a trailer haul to California. I figured It would be best to let the dealer repair it. Good thing I did, for it was covered at THEIR expense.

John W.

Washington