P21DD P20B9 code. Limp mode

Those codes are usually an indication for the Reductant Tank Heater failure that is all to common on these cars. I have heard previously that the Glow Plug Module does in fact provide power to the Reductant Tank Heater so it could be the problem. But, someone else with this same diagnosis ended up needing a new Tank and not the Glow Plug Module.

I hope they are correct in their diagnosis.
Let us know what they do find and fix.

A delete would definitely solve all of your emissions related troubles.

I just had these on my '15 CTD. It was in fact the Def tank reductant heater element. I guess they will know if the Def heater is bad when they replace the module and it still throws the codes? Keep us posted.

When I took car in I told them my scan said def tank reluctant heater and that had already been replaced once 2 yrs ago. They called me and said it was glow plug module. They put module in and had difficult time clearing code causing limp mode. Got another call saying it's reductant heater and tank and want another $400 + in parts. Told them to button it up I'll put that money to a delete kit

gregbonat said:

When I took car in I told them my scan said def tank reluctant heater and that had already been replaced once 2 yrs ago. They called me and said it was glow plug module. They put module in and had difficult time clearing code causing limp mode. Got another call saying it's reductant heater and tank and want another $400 + in parts. Told them to button it up I'll put that money to a delete kit

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Gotta love dealerships that troubleshoot by replacing parts on your dime...

O.P. is your car over 120,000 miles? if not find another dealer because the tank and heater are under 10 year, 120,000 war.

207000 miles. Way over. Been over warranty with every issue GM has had with emissions. Reason I am going delete

NHRA said:

O.P. is your car over 120,000 miles? if not find another dealer because the tank and heater are under 10 year, 120,000 war.

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Is that true for 2014 models too? The emissions systems on this car have been a nightmare.

lorilee1929 said:

Is that true for 2014 models too? The emissions systems on this car have been a nightmare.

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For the tank and heater, as well as the Particulate sensor, yes.

MP81 said:

For the tank and heater, as well as the Particulate sensor, yes.

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and the nox sensor that was impossible for gm to fix for over a year.

boraz said:

and the nox sensor that was impossible for gm to fix for over a year.

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did they fix the NOX Sensor, or did they adjust the control limits for the sensor?

sailurman said:

did they fix the NOX Sensor, or did they adjust the control limits for the sensor?

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sent out a letter aboot special coverage or recall for it, but said in the letter, oh hai, wait til we figure out how to fix it...then a year later had a new tune and you got new sensor, dont recall if it was same sensor or upgraded

Just to add/clarify...not ALL reductant (DEF) tank problems are warranted under Special Coverage 29400.

In 2018 @ 99K miles, I had a P21AB diagnosed as “Reductant Tank Level Sensor Fault”. Tech verified “Level Sensor failed, necessary to replace reservoir to correct.”

I inquired about SC29400 and was told that only covered failure of the DEF heater so I would be on the hook for repair cost.

I didn’t write down the estimated repair quote but seem to recall it was in the neighborhood of $600. Paid $122 for diagnosis and said thank you.

Thanks

MP81 said:

For the tank and heater, as well as the Particulate sensor, yes.

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