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my truck in the sig has a poor quality message level 1. my nox1 is 105 nox2 is 24. on a tech 2 no codes and have ran tank heaters and quality test a regen to no avail. drove truck around. let sit over night. next day drove for 15 min came home ran def tank heaters again and quality test test timed out. shut truck off unplugged tech2 and tried a regen rpms 2500 caused it to stop. tired of messing around with it. am going to try a emisions limited tune and a lift pump and filter.:eek:wned::eek:wned:
 

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would like to clear the message before i install tune. any ideas?
 

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Assuming that you know the fluid is good, and the def injector is working, figure out which NOx sensor is bad and replace it.

Or replace both.

(there is no 'fluid quality sensor' on the truck. Fluid can be tested with a refractometer. Computer is not seeing the change it NOx level it expects from the amount of def it (thinks) it is injecting -- so concludes the fluid is bad)
 

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Assuming that you know the fluid is good, and the def injector is working, figure out which NOx sensor is bad and replace it.

Or replace both.

(there is no 'fluid quality sensor' on the truck. Fluid can be tested with a refractometer. Computer is not seeing the change it NOx level it expects from the amount of def it (thinks) it is injecting -- so concludes the fluid is bad)
I check each jug of DEF with a refractometer before using it. Cheap and easy insurance to make sure the DEF is spot on for Urea %.
 

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Nox sensors have less than 2000 miles on them I have replaced them.
 

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What is the value it is I know 70% down stream or so but my nox is so low anyway. Sometimes the 1 is at 75 and #2 is 4. They fluctuate steady.
 

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I did perform a regen. Where do you calibrate nox?
 

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I believe it's called something like "nitrogen oxide sensor reset procedure"
 

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Discussion Starter #11
I have drove 2000 miles no problem. After changing nox sensors and tank heater. Plugged truck in to 5th wheel while still hooked up to pole power must have spiked through.
 

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The value is on nox1 104 ppm the value on nox2 is 16ppm. It's not going to drop much more than that. Hell it's been down as low as 4ppm on #2. Does any one know what the numbers should be?
 

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Monitor the numbers while driving, have the truck warmed up, and do a hard acceleration followed by a zero throttle coast decel, and the numbers should drop to under 100(number could be incorrect don’t have SI access on phone, going by memory) typically under 10ppm(again by memory could be mistaken). If a sensor does not respond like this, it is faulty.
 

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What DTC’s are you getting? P207F, P20EE, P2BAD

Like oxygen sensors, NOx sensors will not work unless they are at the correct temperature, so they have an integrated heater that is also module-controlled. The power supply to the NOx sensor module is critical to proper sensor operation. In the case of the 2011 Duramax LML (VIN 8) engine, the glow plug control module (GPCM) supplies constant voltage to both of the NOx sensor modules. If system voltage is low, an internal voltage boosting circuit in the GPCM will make up the difference to ensure proper NOx sensor operation.

During a cold start, moisture in the exhaust system can interfere with NOx sensor operation. In this scenario, the Duramax ECM will not turn on the NOx sensor heaters until exhaust temperatures reach a certain threshold and condensed moisture is evaporated. This can result in a delay of up to 5 minutes before both NOx sensors are fully operational.

In the LML Duramax, exhaust oxygen content information is provided to the ECM by NOx sensor 2 to aid in diesel particulate filter (DPF) regeneration. -

When using two NOx sensors in a urea SCR system, the upstream sensor is used to estimate what amount of DEF needs to be injected ahead of the SCR catalyst to achieve optimal NOx conversion. The downstream (post-catalyst) sensor is then used to check the results. Under ideal conditions, NOx conversion will be high and very little ammonia slip will occur.

An adaptive strategy similar to long-term fuel trim (LTFT) is used to determine the duty cycle that the DEF injector should be operated at. Since there are numerous variables (“drift” in component operation) that can affect the amount of DEF that is injected for a given duty cycle, the table is always being rewritten to maximize NOx conversion efficiency. These calculations are made based on signals from the NOx sensors, similar to the way that oxygen sensors are used in a gasoline-engine emission control system. If the correction factor (trim) of the DEF quantity changes too far in either the positive or negative direction, the ECM will set DTCs and turn on the check engine light (MIL).

The Bosch E86 ECM controls the HCI (Hydrocarbon Injector), FRPR 2, DEF pump, and DEF injector. The ECM has more than 160 new DTCs and you can use the Tech 2 to communicate with it.

The Glow Plug Control Module (GPCM) is located on the alternator bracket on the right side of the engine. The GPCM also provides regulated B+ for the NOx sensors and reductant heaters.

When it checks the 'result' at sensor 2 and determines the NOx was not reduced as expected it then assumes the def is 'poor quality'.

This is why a faulty sensor results in the poor def message.

The value is on nox1 104 ppm the value on nox2 is 16ppm. It's not going to drop much more than that. Hell it's been down as low as 4ppm on #2. Does any one know what the numbers should be?
Here is one persons observation.
SEL on codes P20EE, P207F, P2BAD, and others related to NOX sensor performance. Usually when driven and NOX reading monitored sensor 2 will read higher than expected. The def quality codes will set if nox2 is above approx 1/3 of what nox1 readings are. Typically at steady cruise I see nox1 readings of 200-300 ppm and nox1 readings of less than 30 when the def injector is active. One has to make sure that injector is being cycled as there are quite a few times when the ECM does some type of tests and it will let nox2 go high. Another important thing to watch is that on a long decel both nox sensor readings should drop down very close to a 0 ppm reading. If for example nox1 will drop to 0 but nox2 only drops to 60ppm on MULTIPLE decels then sensor 2 is suspect of being skewed.

Service Bulletin
https://static.nhtsa.gov/odi/tsbs/2014/MC-10112163-9999.pdf

Read starting on page 41
MODULE 4
Diesel Exhaust Fluid System Diagnosis
https://f01.justanswer.com/Toolhut/13774ffd-0bcd-4198-b7b8-7f22425af1b4_6.6l+duramax+lgh+and+lml+diesel+engines+(1).pdf
 
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