DEF and Engine Code


ENGINE CODE: SCR NOx Conversion Low

What do you do when your truck throws an engine code that says SCR (Selective Catalytic Reduction) NOx Conversion Efficiency is Low?  Let’s look specifically at a Detroit Diesel Engine code, SPN 4364/FMI 18 – GHG14 as a typical example of any engine design.

Per Detroit Diesel, possible causes:

  • Contaminated DEF (Diesel Exhaust Fluid)
  • Incorrect concentration of urea in the DEF
  • Biased NOx sensor
  • Excessive DEF build-up inside the SCR mixing chamber
  • Over temp after treatment
  • Improper DPF maintenance (Diesel Particulate Filter)
  • Internal structure failure of 1-Box


First – Check Your DEF

The first thing, and the cheapest, is to check if your DEF meets the ISO specification for DEF.  Are you buying an API approved DEF?  API set the standard for making and keeping DEF.  AUS 32 and ISO 22241-1 specifications.  If it’s not API approved – why not?  How are they making it?  Is it right every time?  Is it tested before it’s sent out?  If tested, did an outside party approve it?  The industry knows you can buy prills from China and make DEF, but sometimes, those prills are off spec with materials like formaldehyde or other metals.  The distributor:  do they use HDPE Tanks; Stainless Steel piping; do they filter the product at 1 ppm Absolute!

UREA % by weight 31.8 – 33.2
Alkalinity as NH3 % by weight maximum 0.2
Biuret % by weight maximum 0.3
Insolubles, ppm maximum 20 20
Aldehyde, ppm maximum 5
Phosphate (PO4), ppm maximum 0.5
Aluminum, ppm maximum 0.5
Calcium, ppm maximum 0.5
Iron, ppm maximum 0.5
Copper, ppm maximum 0.2
Zinc, ppm maximum 0.2
Chromium, ppm maximum .02
Nickel, ppm maximum .02
Magnesium, ppm maximum .05
Sodium, ppm maximum 0.5
Potassium, ppm maximum 0.5
Salt-Out Temperature, ° F (° C) 12 (-11)
Recommended Storage Temperature, ° F (° C) 12-86 (4.5 – 26.6)

Flamingo can test your bulk DEF, regardless if you purchased it from us.  We can check the concentration and Refractive Index Value of the DEF.  The concentration can be between 31.8 to 33.2% urea.  The refractive index should be between 1.3814 to 1.3843.  Concentration is easy, but a field test will not catch small particles in the DEF.  Visually inspect DEF, and if you see anything, you have a problem.  An analysis  of some of the metals that might be in the DEF is about a $70 test at a lab.


Flamingo would caution you that if you have a low concentration of Urea, someone may have added tap water, which can ruin your SCR system with chlorine and minerals.  Remember, 1 teaspoon of salt in 5,000 gallons of DEF will ruin it.  This is an ultraclean fluid, with any minerals more than 0.5 ppm causing the DEF to be out of specification.  SCR systems are sensitive and contaminants can collect on the catalyst metals (coat the catalyst) which will hurt the efficiency of the system.  This buildup will affect the way sensors work in the detection of the exhaust stream particulates.  Therefore, commercial DEF is manufactured with deionized or demineralized water. Even adding small amounts of tap water to DEF will cause contamination.  Use of contaminated or diluted DEF can, at a minimum, cause your SCR system to malfunction or even worse can cause costly damage to sensors filters and collectors. The level of damage to the SCR system will be related to the concentration of contamination in the DEF.


Damage to the SCR system can include loss of contact surface area of the catalyst and reduced efficiency of the catalyst and possible secondary engine damage, creation of a sticky deposit or clogging of the DEF injectors. Engine damage may occur if contamination blocks pores in the catalyst where exhaust enters causing increased exhaust pressures. The SCR system may require servicing to restore its function or may need to be replaced. The warranty for the SCR system may not cover replacement as a result of using contaminated DEF.


Keep the DEF clean (after you get it)

Whenever handling DEF, the fluid must be kept clean. If a funnel is used, it must be absolutely clean and free of any contaminants. It’s best to dedicate a funnel (and label it) for DEF only. Spare DEF should be stored in its original container, with the lid/cap secured, to avoid airborne contaminants in the shop. Do not transfer DEF to another container that previously held anything else (oil, windshield wiper fluid, coolant, etc.). If you have more than one tote of DEF, cover the Micromatic fitting on the tote not in use – no dust hitting it.  Avoid cross-contamination! It doesn’t take any extra time to handle DEF properly.


The following steps can help you protect your SCR system and diesel engine.


  • Purchase only the highest quality certified DEF; certification should be located on the container, or can be obtained from the supplier.
  • If you Purchase DEF at major truck stops, from fleet fuel suppliers or from auto parts or large retail stores make sure the filling nozzles are clean and free of dirt.
  • Use only dedicated and non-reactive DEF storage and dispensing equipment because DEF is corrosive to some materials such as carbon steel, copper and brass. (and the metal will get into the DEF!)
  • Use DEF to clean DEF equipment (not tap water if possible – DEF is cleaner!)
  • Store at the recommended 12F to 86F-degree temperature range for maximum shelf life; sunlight and high temperatures will reduce the shelf life of DEF. 90 degrees will allow at least 1 year of shelf life.
  • Check the purity of the DEF over time if you store or manage large volumes.


OK – Its not the DEF.  What now?

“If it’s smokin, the DPF is broken!”

It may be true, if the smoke is black.  The industry is slowly coming to the conclusion that DPF filters should be chemically cleaned / Thermally Cooked / Pulse Cleaned regularly, maybe even every year for medium duty trucks and every 1½  for long haul trucks.  If the DPF gets clogged, it creates back pressure that hurts the engine and eventually the exhaust gas is going to force it’s way out.  A new DPF system will cost you between $3-5,000.  Cleaning it yearly is a lot less than that cost and your engine will run as it is designed.  Just do it.  DPF cleaning on a regular schedule needs to become general maintenance.  If the DPF breaks, and exhaust is getting by it to the SCR system, then the DPF problem may create an SCR problem.  (Note a few Fords, and others, have the DPF after the SCR system)

Excessive DEF build-up inside the SCR mixing chamber

Why does DEF build up happen in the SCR mixing chamber?  Many reasons.  The engine is not running properly, so the SCR system “sees” high NOx and tries to keep up.  Your duty cycle may be low engine speeds with excessive power needs leading to high NOx.  The dosing sensor is broken and the system is putting too much DEF into the mixing chamber.

Sometimes a regeneration in of the Diesel Particulate Filter will help vaporize the DEF buildup in the SCR system.  This is because it gets the temperatures up to vaporize the buildup.  But sometimes the buildup is too much and will require service.

NOx Sensor Biased/Bad

A little history.  In Europe, when they first implemented SCR, before America did, people were defeating the SCR system by just adding water to the DEF tank.  The government’s  attempt at improving emissions resulted in a worse situation for NOx. So when America rolled SCR out, the government required sensors to detect DEF and NOx.  Too much NOx, add more DEF.  NOx low, cut back on DEF dosing.  But then, the OEM’s figured out that if the engine had timing problems, and NOx rose dramatically, the NOx sensor would start dumping DEF in the mixing chamber, even though there was no way it could counter the large amount of NOX.  So the OEM’s have a range of what they allow for DEF dosing.  If the sensor hits too high, the light comes on, and the system hits its limit on dosing.  Should the system believe that NOx emissions are being exceeded past permissible limits and mathematically the treatment cannot be completed within the predetermined dosing ratios, it results in the system setting of a dashboard warning light, typically stating “bad DEF”.  However, it should be noted that the vehicle is not testing the fluid itself, but perceived effectiveness of the SCR system.  To date, most cases we have seen have been the result of an improperly functioning NOx sensor and the fluid is completely within specification.

In addition to the above, things break.  The Sensor can get clogged / blocked / etc.  The sensor gives the SCR system the information to properly dose the DEF.  Bad information leads to bad results.

Over temp after treatment – i.e. EGR System

There are fleets in the industry that are starting to replace EGR systems at 250,000 miles before they break.  Why?  Because experience shows that they are going to break.  Metal that constantly cooks and then cools wears out.  Some would say this is a design flaw, and maybe it is.  But EGR systems are not there yet.  If the EGR system fails, the DPF and the SCR systems are down stream, and the domino’s will fall.

The EGR system uses the cooling system to cool the engine exhaust down before it re-enters the engine.  This puts an extra burden on the cooling system.  In addition, if poor coolant is used and/or the EGR system breaks, engine gases and pressures can enter the coolant system resulting in contamination of the coolant and increasing pressures in the coolant system.  Sometimes it pushes the coolant back away from cooling areas, resulting in failure.  AND, when the engine stops and cools, coolant can be pushed back into the EGR/DPF/SCR systems causing damage.  If you start your vehicle in the morning and see white smoke, this could indicate a big problem.



In 2007, and then in 2010, the federal government added a lot of emission maintenance headaches for fleets.  EGR ($?K), SCR ($6K), and DPF ($3-$5K) systems are costing Fleets 10’s of thousands of dollars every year for every truck.  When the light on the dash comes on, it can mean many things.  The industry is slowly trying to get a handle on maintaining the trucks in the field now and praying for improvements in the design of emissions systems in the future.  Each OEM is having general problems and each OEM has it own unique set of problems.  Information is powerful.


  • Buy API approved DEF from reputable sources
  • Keep the DEF clean – add a filter to your system.
  • Clean DPF regularly – before problems happen
  • Educate Drivers
    • Truck Power changes –> have someone check engine.
    • Problems can cascade from Engine->EGR->DPF->SCR
    • Problems can cascade from SCR/DPF/EGR -> Engine
    • If it’s smoking, the DPF is broken! (black smoke)
      • White smoke may be coolant in the engine/emission systems (or after regen)
    • Adding Coolant – regularly and in a large amounts is a sign of a problem
    • Coolant System may be designed for 7 psi normal – more is a sign of a problem
  • Check for Service Bulletins on your equipment
    • There are known problems for emissions on most engines
    • You need to become aware of the known issues – they may be under warranty.
  • Talk to your Fleet Supplier and ask them to educate you and your drivers.
  • CONSIDER A WIRELESS VEHICLE DIAGNOSTIC SYSTEM – You may want to track your vehicles, but these same systems offer real-time and retrospective reporting on fault codes.  The quicker your mechanic knows of the problem, the better you can protect downstream systems on the vehicle.  Your driver may not catch a difference, but the computer in the truck is currently throwing codes, but no one is aware of it until a system fails.  Remote monitoring of vehicles will be a game changer for vehicle maintenance going forward.


Flamingo Sells:

  1. Lubricants
  2. Ad Blue DEF (API approved)
  3. EGR Cleaners (TC201170 tool + TC201280 + EGR Adapter for engine)
  4. DPF Cleaners (LM5169 + LM5171)



Our DEF is filtered 3 times by us before you get it!

Our DEF comes from Natural Gas from a billion dollar company!

We check our DEF when it shows up.

Our DEF is Fresh!  Within weeks of manufacturing, not a month!

We deliver on dedicated and certified API DEF pumping systems.

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