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I have a 2013 Duramax that of course has the stupid DEF, my check engine light came on Monday and Orielly's said the code it was giving was P21DD but there was no explanation...does anyone know what this means?
 

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Do you know if it's due to weather? I live in AZ it doesn't get TOO cold here but I WAS playing in puddles on Sunday and I thought it could be from that...
 

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No, mine has not misbehaved yet, 25,000 miles, I have a TechII and the GM SI information, just waiting until the day.
You might get under it and unplug, clean & put die-electric grease on them, Then reconnect, since you went through he water.
Did you read the description?
 

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I have 46000 on mine, my husband is going to love me for this one :) I sent him the information on it. It couldn't have been an easy code like replacing a gas cap. Thank you so much for the information!
 

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It's likely that the heater that the code pertains to is faulty - at the dealer we would use the scan tool to monitor the amperage drawn by the heater in question and compare it specs. Can't open SI on my phone or I'd say what that is.

I wouldn't just replace the part without actually testing though.
 

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Found this.
2013 gmc, 16,370 miles, cel on with P21dd code and is currently at dealership for def heater element replacement. Vehicle has been there since April 1st and waiting for part to show up the week of the 14th from gm. So my vehicle will be there over two weeks and not very happy.

Is it under warrenty yet?
 

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Just had this code show up today on my 2013 with 31,300 miles on it.
 

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Mine went south Sunday, it's sitting in Kellogg waiting for the part to get here from Reno. Maybe fixed by Friday, I'm getting prices for a full delete. It's been in the shop 3 weeks already since January for DPF/Emissions issues :mad:
 

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Well the CEL went off and the code cleared on its own:rolleyes:
 

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Well the CEL went off and the code cleared on its own:rolleyes:
Mine comes on like once a week and I clear it and then about a week or so later it will come back on again. Has anyone else fixed the problem with something other than heater replacement? And how much does that element replacement cost? Thanks
 

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Well the code just came back and now it will not clear:banghead:
 

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If you take this to a shop to get diagnosed please post in here. I clear the code like once a week it intermittently comes on for no reason . 😭
 

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If you take this to a shop to get diagnosed please post in here. I clear the code like once a week it intermittently comes on for no reason . 😭
Sure no problem, i am just hope it does not put me into reduced engine power. It is my work truck and I am booked for the next two weeks, so it will be a bit.
 

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Not weather related.

If the tank heater circuit has an open, the heater has failed, or there is a harness/connector problem.
 

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I have replaced dozens of heaters (there's 3). Never had a wiring issue yet. The three heaters are located in the DEF pump, the DEF injector supply line and the DEF reseviour (looks a lot like the pickup on a fuel pump or fuel sending unit in the fuel tank).

Typically diagnosis is checking current draw for the heater in question when it's commanded on, GM has very good specs (don't have have them in front of me now though). Haven't seen one yet that read 0A (indicating an open circuit/damaged wiring) I would install a test light across the connector and command the heater on again, if the lamp lights, bad heater. If amperage is out of spec, bad heater.

Very common.

Lots of guys on here saying "got my tank replaced" and I wonder if all that was replaced was the reseviour.
 

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My 2013 is at the dealership as I type this. They said P21DD is, as we know, an issue with the reduction tank heater. Spec says it should be from 5 to 7 amps, mine is at 3.46 max. They quoted me $679 to replace, I believe the heater plus tank. They say the truck will eventually go in limp mode...I would rather put the $679 towards deleting this system!
 

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You have enough miles on it that it's not covered by the emissions warranty?
 
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