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P20e8

12K views 10 replies 8 participants last post by  fjm568 
#1 ·
So I went up to the local mountains today(Snow Summit has a bike park in the summer), and on the way down(lotta corners) I got the "298mi of DEF left" message, followed only a second or two later by one that said " you've got 99mi before you're restricted to 65mph). At the same time what I guess is the DEF idiot light came on, and so did the CEL. The CEL is what concerns me, as it shouldn't come on just because you've got 300mi of DEF left.
So since I was stuck in my truck for another hour and a half I decided to call Onstar.
The woman gave me the code and its description:
P20E8 The Emissions System is not performing as expected. An issue has been detected in the Exhaust Emissions System which monitors and controls exhaust gases released into the air from the engine. If the vehicle is continually driven with this light on, the emission controls might not work as well, the vehicle fuel economy might not be as good, the engine might not run as smoothly and could lead to future repairs.
I stopped at the auto parts store on my way home and picked up some DEF, and magically when I re-started the motor I had another 298 miles left. The CEL was still on however(the other idiot light was not).
So what I'm thinking is(and I'm looking for opinions from the smart guys on here), when I was throwing the truck around in the corners, maybe the pickup for the DEF picked up some air?
I'm gonna clear the light and see what happens.
TIA
 
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#2 ·
I had this code. Found the truck was too cold for too long and the def was frozen ( I live where it hurts to breath). I put the truck in a heated garage for the night and the problem went away. Obviously not the same issue as yours but what happened is similar, def isn't getting to the exhaust. Sounds to me like your tank was too low as you suggested.


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#5 ·
Found the truck was too cold for too long and the def was frozen ( I live where it hurts to breath).
:surprise:

I wondered this about my 2017 work truck. What temp does DEF freeze?
A. A 32.5% solution of DEF will begin to crystallize and freeze at 12 deg F (-11 deg C). At 32.5%, both the urea and water will freeze at the same rate, ensuring that as it thaws, the fluid does not become diluted, or over concentrated. The freezing and unthawing of DEF will not cause degradation of the product.
So DEF is 32.5% water? or 32.5% def! sheesh...My truck (Kenworth 500HP) uses about 12.5 gallons every 1800 miles.
 
#3 ·
I would reset CEL and wait. It may have had a level sensing issue from the low DEF on downhill curves and decided to set a fault code for you. Let us know if/when the light comes back and if it is same code. Then you can look into it more from there. Only a guess right now without looking deeper.
 
#6 ·
Thanks for the help guys.
I'm gonna go with the DEF being low and burping some air into the system thanks to me playing Mario Andretti, because that's the best theory for my hair(if I worry, it falls out:grin2:).
Cleared the code but driving it around to see if it pops back on will have to wait 'til tomorrow
 
#7 ·
DTC P20E8 Reductant Low Pressure

DTC P20E9 Reductant High Pressure

Circuit/System Description The pressure sensor information is used by reductant control module; this module manages the reductant pressure system driving the PWM signal to the pump (corresponding to a speed set point for the reductant pressure pump) in order to build the pressure in the reductant pressure pipeline after system start*up. The pressure signal is also used to control the reductant pressure in closed loop, to supply a stable value to the reductant valve during the dosing and to empty the reductant pressure line in Afterrun. The reductant pressure is monitored for pressure control governor deviation. The reductant pressure sensor signal is compared with a threshold and a pressure control governor deviation fault is reported to the ECM after a specified time when detected.

Conditions for Running the DTCs
-The battery voltage is greater than 11 V.
-Ignition On or engine running DTC P103F, P1040, P1048, P1049, P1056, P1057, P1058, P1059, P105A, P2047, P2048, P2049, P204B, P204C, P204D, P208A, P208C, P208D, or P214E is not set.
-Reductant Level must not in restriction or empty level state.
-The NOx Reductant Tank Status must not be Frozen and defrosting cycle must be complete.
-The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC
P20E8 The Reductant Control Module detects that the reductant pressure is less than a calibrated threshold for 5 s.
P20E9 The Reductant Control Module detects that the reductant pressure is greater than a calibrated threshold for 5 s.

Diagnostic Aids A leak in the reductant system can be determined by inspecting for a build*up of crystallized diesel exhaust fluid (reductant). Water content in the reductant will affect the freezing point.
 
#10 ·
I had this same thing happen to me. DEF message went away later that day and CEL went away the next day and 6k miles later has never happened again. I did multiple tests on the system using GDS on my laptop and it passed every test.


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