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I recently had the common P21DD code come on for the first time at approx 36K miles. My dealer is telling me the DEF heaters are on a nationwide back order. Code was reset and came back about a week later, which I figured it would. I reset it through my CTS2. Hasn't returned (yet)? Anybody heard of this current back order (I know this has happened in the past)...or know of an ETA of the DEF heaters to dealers?
 

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Does this mean the two in my garage are at a all time high?
 

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Yup mine sat at the dealer from March 1-18th. My issue was the def level gauge but they replaced the whole unit tank/heater/gauge. I was also told def parts were on nationwide backorder and basically the dealer puts the order in to GM and the parts show up when they show up.
 

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I purchased mine for my LML online under GM part number 22902619 and received it in a couple of days (from a non vendor for less than $200, hence no link posted). Google search that number and you'll see some listings pop up. I would assume it's the same part number for the newer systems, maybe someone else can chime in on that.
 

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Just got the P21DD message today.
Will try to get to the dealer tomorrow, but it seems hit or miss to get the part quickly.

I have one week before I move from VA toTX hauling a very heavy toy hauler.

If I have to let it ride, will it go into limp mode on me, or will the light just stay on?


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You should be fine I used my truck for 3 weeks every day before I replaced it.
My check engine light turned off by itself after a week or so.


So you were not clearing the code and it didn’t limp on you?
I have a 1500 mile trip next week with 16k trailer


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I drove my truck daily, towing the tool trailer, with a DEF heater code, for months. No issues

Ultimately that code and the DEF injector pouring fluid into the exhaust is what led me to just delete the thing.

But you should be fine letting the code ride for now. Or stop and have it cleared at a parts store
 

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def heater

My engine light on code reads p21dd
Dealer says GM back order on part
Complain like H and they gave me a rental truck free till completion
My question is is GM replacing the heater with the the original crap or are they upgrading to a new part
 

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Went to the dealership. They confirmed that they could not just order the heater, but the whole tank assembly at about $300.

BUT they also confirmed the back order status ...

They did not charge me a diagnostic fee (~$145) but they did clear the code and wished me good luck on my 1500 mile move to Texas with a very heavy toy hauler.

Drove it the rest of the day and turned it off and on a couple of time during that. No CEL...so here is to hoping it stays off...at least until Texas


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You can't rely on someone else's experience as an indication of what yours will be like. Perhaps theirs had a single failure so the code didn't repeat and just continued to illuminate the CEL until it timed out. Hence no limp. Yours might be a continuous failure that will put you into limp mode at the worst possible time.

I wouldn't leave on the move until I had a good scanner in the truck that could reset the code when needed. The last thing you want is to be in the middle of nowhere and have it limp down to idle. Also don't be without resources on the trip, like coats, a bit of food and some water. Keep your phone charged. If you can't count on the truck you need to count on yourself.

I would have no moral qualms about deleting such a system that is unreliable, un-fixable and can leave you stranded.
 

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You can't rely on someone else's experience as an indication of what yours will be like. Perhaps theirs had a single failure so the code didn't repeat and just continued to illuminate the CEL until it timed out. Hence no limp. Yours might be a continuous failure that will put you into limp mode at the worst possible time.



I wouldn't leave on the move until I had a good scanner in the truck that could reset the code when needed. The last thing you want is to be in the middle of nowhere and have it limp down to idle. Also don't be without resources on the trip, like coats, a bit of food and some water. Keep your phone charged. If you can't count on the truck you need to count on yourself.



I would have no moral qualms about deleting such a system that is unreliable, un-fixable and can leave you stranded.


As for being prepared to survive on the side of the road...I have a fifth wheel behind me on the trip with all the fixin’s...and good Sam road side support.
So that is a blessing...and a curse

The dealer cleared the code and said they didn’t see any logging that would indicate it was going to limp.

I would like to know if I should get some OBD2 scanner before the trip to allow me to clear it if it pops back up, or if that is a fool’s errand.

All that being said, I never got a DIC message, just noticed the check engine light


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If you own a vehicle newer than 1996 you need a scanner. Maybe you can't do much actual work but just knowing what is going on can be priceless. There is a thread on here about which scanner is best. There is no one answer but you can buy a dongle that will bluetooth with your phone for around $50 that will tell you all you need to know and then some. It will let you clear codes so that if it does limp you can unlimp it.

Here is the scanner thread:

https://www.duramaxforum.com/forum/drivetrain/983703-what-best-scanner.html
 

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I have a full DEF system and some exhaust sensors. I removed from truck if anybody wants it for a very small fee lol
 
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