DEF Limp Mode Message

[Jaketab]

2020 Denali 3.0 Duramax with 20700 miles displayed the following warning message.  "DEF Quality Poor"    Then gives the number of miles remaining (70) before vehicle goes to 65 mph speed limitation.   Also says, "See owner manual".    I have always used fresh Blue DEF and always refill when indicator gets just below half.   The vehicle was left at the dealer today.  Hope to know something by tomorrow.  The vehicle went through 1 regen DEF cycle since the tank was topped off 200 miles ago.

No complaints up to now.  The vehicle gets excellent fuel mileage. 

Comments welcome from others who may have had similar problems.

 

Thanks - J Tab 

[redwngr]

Are you using Blue DEF or Blue DEF Platinum??

 

 

 

 

[Jaketab]

Regular Blue DEF only.

 

[redwngr]

On LML, 'DEF quality poor' typically/usually meant that one or both NOx sensors needed to be replaced.

 

They seemed to drift out of calibration.  When the happened the computer incorrectly concluded that there must be a problem with the DEF.

There were many incorrect diagnosis and theories while this was being sorted out.

 

I hope they sample your def -- and presumably find it is ok. Assuming it was bad and just replacing it was one of the reasons there were some many issues with LML. (of course it wouldn't stay 'fixed' as they drifted in and out of range)

 

Post back what they find with yours.

 

[Jaketab]

redwngr - Thanks for the tip.  The service rep just called.  Said there is a see-through window on the DEF tank and what they are seeing by using a flashlight is the DEF has a pinkish color.  That may or may not be an illusion by reflection of the light beam.  They are now in the process of taking a sample to confirm contamination.  If the DEF was contaminated by external means, it most likely will not be covered under warranty.    If the fluid is contaminated, it would have to be an act of vandalism.   I have always questioned why there is not a locking mechanism on the fuel door to prevent such a happening.

 

J Tab

 

[redwngr]

Vandalism to vehicle fluids has always been a possibility -- not just to def.

 

If it was vandalism your comprehensive insurance should over it. 

 

 

Any change it got some diesel in it?

 

 

I was a fan of the DEF fill being under the hood -- to keep them separate. 

Of course lots and lots of posters wanted GM to do like the 'other guys'....and they got their way... 

 

The other thing that could happen is def in the fuel tank.

Fwiw, if DEF is ever put in the diesel tank -- do not even turn the key on, as the in tank fuel pump will force def thru the fuel system....

 

https://gm-techlink.com/?p=16581

Diesel Exhaust Fluid Contamination in the Fuel System

July 29, 2022

Poor diesel engine performance conditions, such as hard starts, rough running or hesitations and low fuel pressure, may be the result of fuel system contamination. The most common sources of contamination are other automotive fluids, including gasoline, engine coolant and engine oil. In diesel engines, one other culprit of fuel system contamination is Diesel Exhaust Fluid (DEF), which may be mistakenly added to the fuel system by owners. (Fig. 1)

 

Fig. 1

 

These fuel system contamination issues may be found on many GM vehicles equipped with diesel engines (RPOs LM2, LUZ, LH7, LGH, LWN, LML, L5P, L5D), including 2010-2022 Express, Savana; 2011-2022 Silverado; Sierra; 2014-2019 Cruze; 2016-2022 Colorado, Canyon; 2018-2019 Equinox, Terrain; 2019-2022 Silverado 2500HD/3500HD, Silverado 4500HD; Sierra 2500HD/3500HD; and 2020-2022 Tahoe, Suburban, Yukon and Escalade models.

Fuel system contamination can affect the performance of the fuel pump module, especially the spring and strut components, fuel level sensor and the fuel pump. (Fig. 2)

 

Fig. 2

 

Filling the DEF Tank and Fuel Tank

Some customers may add DEF to the fuel system in error due to the location of the DEF fill port. For example, on some full-size trucks, the DEF fill and fuel fill are both located behind the fuel fill door. It’s important to show customers the owner’s manual and other product materials that include details about the correct way to fill the DEF tank and how to distinguish the fill port for DEF from the fuel fill.

To ensure the correct system is being filled, only remove one cap at a time. The DEF fill cap and the fuel fill cap (if equipped) should not be removed at the same time. With the capless fuel fill system, extra caution should be used. The DEF system uses a blue cap while the fuel fill is green.

Fuel System Cleaning

If diesel fuel is mixed with DEF, or if DEF or gasoline is added to the fuel tank, it may lead to repairs that may not be covered by the New Vehicle Limited Warranty.

If the fuel tank is accidentally filled with DEF:

• Do not turn on the ignition
• Do not start the engine
• Do not drive the vehicle

As soon as the ignition is turned on, the fuel pump will be engaged and contaminated fuel will be sent into the fuel system, which may potentially damage the entire system. Inform customers to have the vehicle towed to the dealership or a qualified service facility.

DEF is a corrosive fluid that tends to form deposits on components. If the in-tank fuel pump has been run, then contaminated fuel has been pumped through both the low-pressure system and high-pressure pump.

• If the engine has been cranked, the entire fuel system from the fuel fill pipe to the high-pressure fuel pump, fuel rail, injectors, injector return fuel lines, high-pressure fuel pipes and low pressure return lines must be replaced.
• If the engine has not been cranked, the system from the fuel fill pipe to the high-pressure fuel pump as well as the high-pressure pipe from the pump to the rail must be replaced along with the low-pressure return lines.
• If the in-tank fuel pump has not been run, the fuel fill pipe, tank and fuel pump module should be replaced.

Refer to Fuel System Cleaning in the appropriate Service Information for complete details.

Fuel Pump Module

GM has seen a number of failed diesel fuel pump modules that have been returned under warranty due to DEF contamination of the fuel system. DTC P1029 (Fuel Pump Phase U-V-W Circuits Open) set in the Engine Control Module (ECM), which indicates a loss of continuity with the fuel pump, is a potential sign that DEF was added to the fuel tank.

Other signs of contamination can be seen on the fuel pump module itself, where there may be corrosion of the steel and aluminum components. (Fig. 3)

 

Fig. 3

 

DEF contamination also may leach between the plastic portion of the fuel pump and the terminals, leading to fractured terminals and terminal failure. (Fig. 4)

 

Fig. 4

 

Recognizing DEF Contamination

Without removing the fuel pump module, it may be difficult to recognize DEF in the fuel tank. White crystals can appear in the form of residue (similar in appearance to salt) when it dries on components. (Fig. 5) Of course, the residue cannot be seen in the contaminated fuel.

 

Fig. 5

 

Taking a fuel sample may be one of the most effective ways to determine if there is contamination. Taken from the bottom of the fuel tank or fuel pump module reservoir, the sample may show a cloudy mixture when it’s shaken. Any DEF in the sample will usually separate from the fuel within 20 seconds and sink to the bottom of the sample. (Fig. 6) The same reaction occurs on a larger scale in the fuel tank, where the fuel pump picks up the contaminated fuel.

 

Fig. 6

 

TIP: New testing procedures for contaminated fuel are currently being reviewed. Look for additional details about fuel testing coming soon to Service Information.

When servicing a vehicle with contaminated fuel, also check the fuel filter, which has a reservoir that collects water from the filter. The fuel filter reservoir should be drained.

DEF and Fuel Don’t Mix

It should be stressed to customers that if a mistake was made and DEF was added to the fuel tank, the vehicle should not be driven to the dealership for service. The vehicle ignition should not be turned on and the vehicle should not be started. These actions will help limit any damage to the fuel system from contaminated fuel. The New Vehicle Limited Warranty may not cover any fuel system repairs related to fuel contamination.

Edited August 5, 2022 by redwngr

[Jaketab]

Update on DEF contamination.  The local dealer said the DEF was contaminated by symtoms of gelling.  Visual exam only.  The service rep also mentioned crystals.   The repair would be $3000 not covered under warranty.   Horse Crap.

There is no way I have contaminated the DEF.  I can see where it would be easy to put DEF fluid in the diesel fuel because the filler has no cap.  However, in order to contaminate the DEF with Diesel fuel, one would have to remove the blue colored DEF cap and "consciously" insert the fuel nozzle into the DEF filler.

Bottom line - I called the purchase dealer 100 miles away.  They are sending a flatbed truck to pick up my Denali and repair the truck.  It will be later next week before I know their findings.

I now question whether or not the local dealer is trying to gouge more money by not repairing under warranty.

Thanks all for replies.

 

[DDION]

Perhaps this will help bring some clarity to the issue of resolving issues with DURAMAX protective speed restrictions due to DEF quality issues.  Earlier this summer I had an DEF contamination issue with my 2020 GMC Sierra 3500 that resisted every fix posted on this forum and others.  Draining the DEF tank to eliminate all contamination was an obvious first step, but not as straightforward as you might expect.  There were several posts suggesting siphoning the tank by entering through the filler connection on the top of the tank because there is no drain built into the tanks to facilitate such an activity.  That helped for a brief period of time only to have DEF quality issues continue to occur.  Assuming I had not gotten all of the contaminated fluid out of the tank I went the extra mile and ordered an electric siphon pump and evacuated all of the fluid possible by going through the filler connection on the top of the tank.  Again that didn’t resolve the issue and it persisted to the point the speed lock out was already limiting the truck to 55 mph.  
 

Frustrated with the issue I took the truck to the local GMC dealer for their intervention.    About an hour into working on it they called to advise me the truck would require replacement of the entire system at a cost of $6,100.  My answer was simply for them to button things up and return it to me.  Resolving the issue would require an understanding of how the DEF system was designed to function particularly how the system detects DEF quality.  What I found was that the majority of the parts in the system were static in their function such as the DEF injector and diesel particulate filter.  The majority of the active elements in the system are actually found inside the DEF tank itself with the reductant control module mounted on the top of the tank.

 

With respect to determination of DEF quality, the system uses two components to assess its state.  There is an ultrasonic sensor built within the tank itself and the system also uses the lower NOX sensor after of the diesel particulate filter.  It was obvious to me that there was still contamed fluid in the DEF tank after I had pumped it dry.  When I removed the tank to attempt to empty it manually I found there was indeed a substantial amount of fluid still in the tank that I could not get out.  There are obviously baffles within the tank that prevent extraction.  A replacement tank was acquired and installed.  That cleared all of the codes however the DEF quality indication on the dash remained as well as the speed reduction lock down though now it had reached the dreaded 5 mph limitation. 
 

I ran diagnostics and reset the ECM to factory defaults, disconnected the batteries, and even attempted to manually initiate a regeneration of the reductant system.  Nothing cleared the DEF quality condition or speed lockdown.  That focused my attention on the sensors upstream and downstream of the diesel particulate filter.  There are two exhaust temp sensors and the lower NOX sensor.  I replaced the two temperature sensors first to see if they would clear the condition.  No luck.  I then replaced the lower NOX sensor and evaluated the impact.

 

The DEF quality indication remained even though no error codes were present.  What I suspected was that a small amount of contamination still remained in the lines from the tank to the DEF injector so I elevated the engine RPMs to 2,000 for approximately 10 minutes.  As I backed down the throttle the DEF quality indication cleared and the speed lockdown cleared.  The net of it is this, if a DEF contamination exists the only way to assure no contaminates remain in the tank is to pull and replace the tank.  If the DEF quality indication does not clear the lower NOX sensor will likely need to be replaced as that is the only other component in the system that influences the system determination of DEF quality. 
 

Hope this helps.  It cost just under $1,000 to restore my truck.  Not cheap but I didn’t have to part with another $5,100 to get my truck back in prime shape.  Best of luck to you all.

Edited September 19 by DDION