DEF Injector Concerns 2019 GM Duramax 2.8

Paul Owner/Technician Wisconsin Posted   Latest  
Resolved
Driveability
Emissions
P249D — Closed Loop Reductant Injection Control At Limit - Flow Too Low
P20EE — SCR NOx Catalyst Efficiency Below Threshold Bank 1
P11DC

This vehicle has about 75000 miles on and is setting codes for Cat efficiency test below threshold. Because we just replaced the DEF Injector 5 weeks ago, we are thinking NOx Sensor 2 has failed. But we wanted to retest the injector first. We ran the DEF Injector Quantity test with both an aftermarket scan tool as well as the GDS. Specs call for a minimum of 20ml at the end of the test which lasts 5 minutes. We are getting around 12ml. Next test is to measure pump quantity and we should get a minimum of 30ml at the completion of the test which we do get. We had just replaced the DEF Injector 5 weeks and 4000 miles ago. Tests results say to replace the DEF Injector. We put a new GM DEF Injector in and have the same test results. Desired and Actual DEF Pump match at 72 psi. Scoped the pump and have a great pattern. Kind of stumped and hoping someone has run into this before. We did not find any TSB's or Reflashes that point to this. 

0
Interesting
Caleb Diagnostician
Indiana
Caleb
 

Does the DEF line have a restriction or are you testing pump volume at the injector end of the tube?

0
Ð Awarded
Christopher Technician
Saskatchewan
Christopher
   

Don't have much input on the automotive side but have dealt quite a bit with the HD SCR systems… For DEF quantity tests it's usually best to do them in multiples, repeating the same test… With no circuit codes DEF doser, DEF pump pressure ok, and correct larger quantity tests confirmed I would suspect there may be another issue rather than a failed doser… Usually those codes you listed are set…

+2
Ð Awarded
Helpful
Rick Technician
Virginia
Rick
 

Did you monitor the inlet and outlet Nox readings with SCR temps above 300 /350 degrees F ? If outlet ppm is staying equal or above the inlet your SCR is not functioning. Pull and send out for cleaning.

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

This sounds like a choked SCR. Run a regen in the system to burn the particulates out of the system. If the owner is letting it idle excessively, they need to quit it. These systems are meant to be run hot constantly. If this is a short trip delivery vehicle, you can expect to see more of this happen. You should have a regen procedure in the service information or in your scanner menu. (some…

0
Ð Awarded
William Owner/Technician
Nevada
William
 

Perform multiple MANUAL regens between 3 - 6 times. after a couple look at data to see upstream and downstream pressure readings.

0
Ð Awarded
William Technician
West Virginia
William
   

All your codes point to a possible leak in the charge air system. With 75000 miles, and a new DEF injector, I doubt you have catalyst issue. Perform a charge air leak test. Refer to #17-NA-194.

0
Ð Awarded
Paul Owner/Technician
Wisconsin
Paul Resolution
   

We have this fixed. It was #2 NOx Sensor. When I ran the SCR Bay Test and watched my NOx sensor readings, number 2 NOx sensor would drop to a -100 ppm. Replaced the sensor and reran the test and the sensor never dropped below 0ppm. Alos, when I ran the test, it would fail because of #2 NOx sensor. What we do not know yet is why the SCR Injector fails the quantity test test as per GM. Next one I…

+1
Resolution Ð Awarded
Helpful
Thanks
Caleb Diagnostician
Indiana
Caleb
 

Nice fix Paul! IIRC the spec you gave for the DEF injector flow is the same as the 6.6 HD trucks. My guess is SI is wrong and that the DEF injector flow rate you observed is correct for that application.

0
Ð Awarded
Marlin Technician
Oregon
Marlin
 

Probably because what an engineer requested for flow and what actually got used as the production design are not the same. It certainly seems sometimes that the SI writers operate in isolation.

0
Ð Awarded
Rex Technical Support Specialist
Ohio
Rex
 

One thing to try on NoX sensors. Disconnect the doser and run to temp. With no DEF injection NoX readings should equalize. I have two really nice Cummins Docs from school bus seminars. The one has an excellent layout of the whole aftertreatment system. A 6.7 ISB Cummins Coffee Table Book. Only one I have ever seen. If you want give me an e-mail. Or I could try putting up a dropbox link on here…

+1
Ð Awarded
Helpful
Michael Technician
North Carolina
Michael
   

Rex could I get a copy of these? …

0
Ð Awarded