2012 Chevrolet Silverado Reductant Issues

Simon Diagnostician New Zealand Posted   Latest   Edited  
P20B9 — Reductant Heater "A" Control Circuit/Open
P2BAD — NOx Exceedence - Root Cause Unknown
P20EE — SCR NOx Catalyst Efficiency Below Threshold Bank 1
P204C — Reductant Pressure Sensor Circuit Low
Dash Warning Light/Message


2012 Chevrolet Silverado Vin:1GC4K1C81CF194509 

Im afraid that we dont have many of these vehicles over this side of the world so I need some advice from you guys.

This truck came in with the MIL on and a dash warning message 'SERVICE EXHAUST FLUID SYSTEM'

A scan showed P20B9 reductant heater circuit 1 heater control.

After removing the reductant tank I checked the heater circuit which had was open circuit. A new one was ordered and fitted.

I cleared all vehicle DTCs but the dash warning message remains. There are no present DTCs but in I/M System Information, Test DTCs, there are these codes which I dont have any option to clear.

P20B9 reductant heater circuit 1 heater control

P2BAD exhaust NOx concentration high

P20EE NOx catalyst efficiency below threshold

P204C reductant pressure sensor circuit low voltage

In I/M System Status it shows tests that have a YES/NO for COMPLETED, only MISSFIRE shows completed.

I have performed extensive test drive in the hope these test will complete but they havent. 

Using the Tech 2 I have performed all the resets available but I still cannot get the warning to go out.

Live data shows the heater circuits working correctly.

Any direction on this vehicle would be great.



Gustavo Mobile Technician
Gustavo Default

Hi see if you can command the GPCM reductant heater 1,2 or 3 on and of with the scan TOOL​.​ OBSERVE the scan tool gpcm reductant heater 1,2,and 3 current PARAMETER​.​ THE reading should be between 5-7 amps for heater 1 and for heater 2 between 0.75-2 amps and 1.5 to 3 amps for heater 3

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Justin Owner/Technician
Justin Default

I don’t have my computer with me right now. But there was a computer flash update for the early duramax for a few of These codes I believe. Sometimes I have had to force regen to get all lights to go out after a fix.

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Gustavo Mobile Technician
Gustavo Default

You have a test that you can do with the scan tools on the output control menu and follow the instructions call it "reductant system malfunction warning test"

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Kevin Manager
Kevin Default

This message is a latched message until all of the enabling criteria have been met. Just like Gustavo said, you need to command on each heater individually. I typically command on each heater, in order, for 15 seconds each. After commanding each heater on, I then drive the vehicle and the message usually turns off. If can be a bit challenging when this occurs during colder weather, but if you…

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Simon Diagnostician
New Zealand
Simon Default

Hi, many thanks for that, after powering the heaters the warning light went out. I tried to perform a RFQT (Reductant Fluid Quality Test) but that failed. I then tried a regeneration and that failed also. I checked on GM ACDELCO for updates and then performed the required updates. After that I could perform a successful regeneration. Again, many thanks for all your help guys, Simon

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Joe Manager
Joe Default

Simon, Please read the information below. I am also assuming that you replace the DEF fluid with new and did not reuse the old fluid. (Possible contamination) We had a support case similar to this recently. One of the small print items technicians often overlook is that the ECM requires a power down between each RFQT (Reductant Fluid Quality Test) The Reductant Fluid Quality Test (RFQT) may…

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Joel Diagnostician
Joel Default

I replace one of those heather unit recently, after you replace them command them on as they said the 3 of them, also there is a functional test to reset parameters on special functions on gpm, I also forece regeneration.

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Josh Service Manager
Josh Default

Command heaters 1,2,3 on and then perform a reductant fluid quality test, if light still doesn't go out, test drive the vehicle for at least 40 miles with no tech 2 attached--repeat no tech 2 attached. if THAT doesn't do it, you can try to reprogram the ECM because sometimes it get stuck in this mode, at least that is what TAC has told me and also has worked for me multiple times.

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