# P21AB Help



## Rivergoer (Mar 30, 2017)

Got a CEL, Scan Gauge says P21AB. I’m on the road using cell phone and having trouble searching site for info. 

What does this this code mean please?

Will car go into limp mode? (Still have about 200 miles to get home to my dealer)

Am I still covered if parts are involved?

2014 CTD 99,570 miles 

Thanks in advance


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## MP81 (Jul 20, 2015)

Based on what I found over on a Duramax forum, there was a TSB that the culprit could cause this code:

"TSB/Campaign Number 11326 - Some Silverado and Sierra HD vehicles may experience SCR issues involving DEF tanks that were built with low internal resistance, causing DTC codes P21AB, P203D or P21BO. Corrective action would be to perform campaign 11183B and if problem is not corrected, replacement of entire DEF tank would be necessary."

So, if it is, in fact, the DEF heater, that should still be covered under the 10 year, 120k mile special coverage warranty.


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## pacolino (Aug 1, 2015)

Rivergoer said:


> Got a CEL, Scan Gauge says P21AB. I’m on the road using cell phone and having trouble searching site for info.
> 
> What does this this code mean please?
> 
> ...


Hey, this is a DEF level sensor B circuit. Could be a bad connection you may want to check all connectors or the level sensor itself is faulty. You need to make sure you have enough DEF in your tank to make it safe home.

Sent from my SM-G930W8 using Tapatalk


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## Rivergoer (Mar 30, 2017)

MP81 said:


> Based on what I found over on a Duramax forum, there was a TSB that the culprit could cause this code:
> 
> "TSB/Campaign Number 11326 - Some Silverado and Sierra HD vehicles may experience SCR issues involving DEF tanks that were built with low internal resistance, causing DTC codes P21AB, P203D or P21BO. Corrective action would be to perform campaign 11183B and if problem is not corrected, replacement of entire DEF tank would be necessary."
> 
> So, if it is, in fact, the DEF heater, that should still be covered under the 10 year, 120k mile special coverage warranty.


Thanks! That aligns with the limited info I could find. 

I believe that’s SC #29400?


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## MP81 (Jul 20, 2015)

I do believe so, yes.


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## Rivergoer (Mar 30, 2017)

pacolino said:


> Hey, this is a DEF level sensor B circuit. Could be a bad connection you may want to check all connectors or the level sensor itself is faulty. You need to make sure you have enough DEF in your tank to make it safe home.
> 
> Sent from my SM-G930W8 using Tapatalk


Thanks guys. 

DEF level shows OK. I put 2.5 gal in about 5,000 miles ago when level read 25%. 

I pulled over in the middle of the desert (29 Palms Airport, for you Marines our there) and checked the DEF wiring. All appeared solid, clean like it was from factory. Also opened and resealed the DEF filler cap. 

Still have the P21AB upon restart. 

Will call or stop by dealer and update later.


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## sailurman (Sep 29, 2016)

AS long as the countdown hasn't started you should be good all the way home. Drive Safe.


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## Rivergoer (Mar 30, 2017)

Made it back home, no issues. Thanks for the help today.

I pulled over, reset the code with the Scan Gauge. Shut down and waited 5 minutes. Restarted and no CEL, no codes. 

Drove the final 50 miles with no CEL, even with a couple of additional stops just to be sure. Also had a successful Regen along the way.

So the emissions system appears to be functioning as normal.

Since the P21AB seems to be DEF heater/sensor related, it won’t be covered under my PT warranty which is set to expire in another 250 miles. So I’ll wait awhile to see if the issue resurfaces.


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## pacolino (Aug 1, 2015)

Rivergoer said:


> Made it back home, no issues. Thanks for the help today.
> 
> I pulled over, reset the code with the Scan Gauge. Shut down and waited 5 minutes. Restarted and no CEL, no codes.
> 
> ...


I wouldn't wait until your mileage pass the warranty, I would bring it to dealership and claim it, they may change your DEF tank under warranty. They did to my 2015 CTD.

Sent from my SM-G930W8 using Tapatalk


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## Rivergoer (Mar 30, 2017)

pacolino said:


> I wouldn't wait until your mileage pass the warranty, I would bring it to dealership and claim it, they may change your DEF tank under warranty. They did to my 2015 CTD.
> 
> Sent from my SM-G930W8 using Tapatalk


Your DEF tank was covered under Powertrain Warranty, not the Special Coverage?


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## Rivergoer (Mar 30, 2017)

One more question, even though I cleared the CEL, that P21AB code will still be retrievable by the GM mechanic, right?

My Scan Gauge no longer shows any codes.


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## MRO1791 (Sep 2, 2016)

Rivergoer said:


> One more question, even though I cleared the CEL, that P21AB code will still be retrievable by the GM mechanic, right?
> 
> My Scan Gauge no longer shows any codes.


That is the downside of doing a code clear, they won't see it. I do believe the special coverage is for this issue. My 2015 had it and all work was done under warranty. Without an active code it could be dicey getting the service department to work it under warranty. 

Sent from my Moto G (5) Plus using Tapatalk


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## boraz (Aug 29, 2013)

Rivergoer said:


> One more question, even though I cleared the CEL, that P21AB code will still be retrievable by the GM mechanic, right?
> 
> My Scan Gauge no longer shows any codes.


its still retrievable

clearing codes doesnt mean erasing history of the codes.

some codes are only clearable x times, clearing more than that puts into limp mode


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## Rivergoer (Mar 30, 2017)

Got the P21AB again this evening upon start after sitting for a week. 

Taking it in to Chevy dealer Monday, will update with results.


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## Rivergoer (Mar 30, 2017)

Dealer says P21AB is faulty DEF Level Sensor. Requires complete tank replacement $600. 

Not covered under power train warranty or Special Coverage 29400. 

I still have 20k left on the special coverage so I’ll pay the $122 diagnostic fee and wait till the infamous DEF heater fails.


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## MP81 (Jul 20, 2015)

The level sensor isn't just in the reservoir? 

What a pain in the ass.


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## IndyDiesel (May 24, 2015)

That’s crazy, although with gen 1 the def lasts like 20k miles full to empty. Will the computer think it’s low when it’s not and give you a countdown? Mine went bad around 40k miles or so and was the def heater and replaced under special warranty.


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## Rivergoer (Mar 30, 2017)

IndyDiesel said:


> That’s crazy, although with gen 1 the def lasts like 20k miles full to empty. Will the computer think it’s low when it’s not and give you a countdown? Mine went bad around 40k miles or so and was the def heater and replaced under special warranty.


DIC currently shows DEF Level OK. That matches with my estimation since last DEF fill.

So it appears the code is likely some sort of intermittent level sensor failure, but not enough to affect the DIC readout.

I still could be wrong but the car doesn’t spend much time in below freezing temps so I don’t expect the DEF Heater to ever fail. I may never get to utilize the Special Coverage before reaching 120K.

The next question is will I be able to continue clearing the P21AB code without issue? Or will the cumulative effect of multiple codes eventually lead to dreaded ‘limp mode’. 

Time will tell...


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## rescueswimmer (Mar 28, 2013)

Mine failed at 110K miles for the second time was covered under GM's emissions extension or what ever that crap related to the DEF tank was they sent us in the mail. That is why I did the Delete for that reason.


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