The frustrating thing is that we did see over 70% difference between pre and post NOx sensor readings. All was good in the program but it needed updates for the message to erase. Please note that after the NOx sensor was replaced, there were no DTCs. There was a SCR light on the instrument cluster but no MIL light. Just the messages about Exhaust Fluid.

Lesson? As we have seen already on Ford Powerstroke 6.7L, the Duramax LML 6.6L may often require reflash of the ECM when there are no DTCs and a SCR light on. Procedures do call for the Reductant Fluid Quality Test to be ran but if no success and there are no DTCs, reflash ECM and run again.

Note that the SCR light simply is telling the technician that the ECMs program is not satisfied with the NOx reduction attained. 


Engine oil has been one of the most controversial topics to discuss both by the diesel and

working technicians.

Which oil to use? What is the best engine oil? Which weight and should I use synthetic or semi synthetic

blends or conventional? Everyone has an opinion about this. I often have needed to teach customers what they should use. However, if you really want to make the best decision, then base it on facts. As a diesel truck owner, I have a 2006 Ford F-350 with the 6.0L Powerstroke engine. I don’t drive it as often as I used to since I have another vehicle. It has the original fuel injectors, high pressure oil pump and IPR valve, and has about 109K miles. I do change the oil often and have seen the benefits of that. Having recently driven it to and from Denver, CO, I noted that I was getting about 20 MPG and at worst of 17 MPG. Not bad for a 2006 F-350 truck with 1,000 pounds in the bed.

Technology is rapidly changing with diesel and gasoline applications. Diesels with their huge horsepower and torque ratings, along with gasoline applications which utilizes s and turbocharging, are meeting emission standards. It is not surprising to see over 500 horsepower available on a gasoline powered vehicle.

In diesel applications, we see the use of an extensive aftertreatment system that has evolved with more hardware and sensors used and that adds substantial cost to any issue with the engine or the system itself. This has put a heavier emphasis on the maintenance of the vehicle. I have had customers come in with engine failures where they were told that the engine needs to have the oil changed at 15K miles. These are the same customers that pushed the issue and changed their engine oil past the 15 thousand mile mark to 18 thousand miles.

I am old school, and my professor used to say that you can never change our engine oil enough. 15W-40 was the oil of choice for diesel applications, but the recommended weight is now changing. New light duty diesel trucks now use 10W30 and 5W-40. And for cold regions, the recommendation is for the use of 0W-40.

There is CK-4 and now FA-1 engine oil designations.

Before I continue please do not reinvent the wheel when it has been invented.

In forming your opinion of engine oil, the question to really ask is what is it based on? Blogs? Internet articles? Are you informed and educated on the subject?

Technicians that are working in the trade do have serious opinions on what they consider real recommendations they give about vehicle maintenance. The fact is many do not even have an education of any kind. Most working technicians have little education and one certification from ASE does not qualify for bumper to bumper technician. Ask for your technician’s education, certifications and experience. Really ask the right questions! What qualifies a competent technician? Lately I hear technicians called Master Techs with no education or certifications of any kind. 

​The fact is a competent technician who has an education on electrical/electronics, engine management, a bit of science and hydraulics plus experience can give an informed recommendation on what and who to use not to mention when.For example, we do not recommend any kind of synthetic oil since we have seen numerous premature engine failures due to synthetic oil use. Now don’t misunderstand me, synthetic oil is good to use but the question begs, what kind of environment is it working in? Diesel engines that are all turbocharged in diesel trucks and cars today create with time serious crankcase pressure. Crankcase pressure better known as blowby gases are created from piston rings sticking or wear on the cylinder and rings.

Engine oil has several functions. It carries heat, lubricates, absorbs shock and cleans an engine. We have had engine oil tested where the oil lubrication package in the oil itself is done with a truck with as little as 1,100 miles on it. The point is there has been a relationship associated between synthetic oil and extended oil change intervals. In other words, the thought is, use synthetic oil and you can extend your oil change intervals. The fact is engine oil does not really get worn out, it gets overloaded. Blowby gases are constantly overloading the engine oil and slowly or rapidly depending on engine wear and operation.To add more headache let me present a true diagnostic nightmare. A customer brings in a 2012 Ford F-350 Dually Diesel with a 6.7L Power stroke. Our diagnostic led us to  ... continued here ...


When diagnosing fuel, smoke, or frequent regeneration issues, you can observe where the fuel setting is at. If the percentage is over plus or minus 10 percent, then that means there is an issue. If the fuel injectors are contaminated, the programming will add more fuel.  You can diagnose but ensuring that desired and actual fuel rail pressure are correct and that there are no fuel contamination issues.  In other words, you have checked the basics of common rail engine diagnosing.

Let’s role play, you are diagnosing an issue with frequent regenerations, you have checked all the basics, you can observe SFT and verify that all cylinders are in specification. If you have an issue can one cylinder with excessive change in fuel trim contribute to frequent regenerations? Remember that we have diagnosed many diesel issues by the amount of smoke that is visible. Diesel Oxidation Catalysts and Diesel Particulate Filters have masked or cleaned the exhaust thus causing frequent regenerations. Analyze the SFT and confirm if all fuel trims are within specification.

Please keep in mind that excessive crankcase blowby gases can contaminate or coat the catalyst substrate and cause regeneration issues. Turbochargers with oil leaks will contribute as well.


Do you know why there is no check engine light and codes set when a SCR light is on?

We just finished with a 2012 GMC Duramax LML where the reductant fluid quality test was timing out and causing headaches after the installation of one of the NOx sensors. There were no diagnostic trouble codes (DTC), the vehicle was displaying the Exhaust Fluid Quality Poor message and derated to 55 mph.

I read and followed the diagnostic procedure over and over plus read on service information on what techs were discussing regarding this issue. We were on the third quality test which can take up to 70 minutes which times out with no reason given in the PIDS. As I have instructed on this issue, we had to have it reflashed with the latest files from GM. Once flashed, ran quality test again and within minutes, it passed and messages all gone.


The Powerstroke 6.4L is now over 11 years old now and more are probably entering your drive in service

facility with issues. Fuel mileage complaints are very common along with regeneration issues.

The question questions asked many times over is how frequent should a regeneration take place. This is a

difficult questions to answer since there are so many variables.

​I have always stated that the proper function of an aftertreatment system is based on the condition or operation of the engine itself. The frequency of regeneration events are affected by low compression, boost leaks, excessive oil consumption, injector and fuel pressure issues. Driving conditions and habits contribute as well.   

Fuel Trim, better seen on a scan tool as SFT, has been around gasoline engines for a long time. Closed loop fuel systems used on these applications were equipped with oxygen sensors to inform the engine computer or ECU when there was excessive or reduced amounts of oxygen in the exhaust. In turn the ECU would command more or less fuel by changing the pulse width to the gasoline fuel injector. Open loop meant there was no feedback from the oxygen sensor due to the fact that the sensor was too cold or the engine may have been too cold. Heated oxygen sensors have aided in faster warm up to attain closed loop faster in order to maintain fuel control and economy.

Diesel engines incorporate similar controls with common rail injection. In is important to note that common rail fuel strategy takes place changing fuel pressure and pulse width. Programming in the ECU allows for constant fuel delivery changes due to engine load and speed. At idle the 6.4L engine management ECM (engine control module) uses the crankshaft position sensor (CKP) to measure the angular velocity of each power stroke of each cylinder in its firing order. The main input for short term fuel trim (SFT) is the CKP sensor. Oxygen sensors are not used in diesel engines for closed loop fuel control. In making it easy to understand, the sensors such as the engine coolant temp (ECT), the Manifold Absolute Pressure (MAP), the Inlet Air Temperature and other sensors inform the ECM in order to start fuel injection and program a desired amount. When the engine reaches operating temperature over 185 degrees F, the ECM will observe the angular velocity of the crankshaft at idle. As the engine crankshaft is rotating, the ECM knows its position thanks to the Camshaft Position Sensor (CMP). The ECM monitors the angular speed as each cylinder fires in its firing order. Number one fires, number two fires and so on in its firing order. The ECM assimilates if there was too much or too little angular speed and will adjust fuel timing, pulse width, fuel pressure to balance all cylinders to contribute equal power. Let’s say number 4 cylinder is weak due to lower compression. The ECM will add more fuel to that cylinder to increase power. On the other hand if a cylinder has too much power contribution due to excessive carbon buildup on the top of the piston, this will add more compression. The ECM will reduce fuel to this cylinder.

It is a form of a closed loop system since the CKP is providing feedback to the ECM if there is too much or too little power contribution from all cylinders.

You as the technician can view individual fuel trim (SFT) on the scan tool such as the IDS on Powerstroke 6.4L engines. It is important to emphasize that engine must be at operating temperature and at idle. This can be used to interpret if there is a compression issue, an injector issue or mechanical issue.

The scale Ford Motor Company uses on these engines is a percentage. The common specification is plus or minus 10 percent. Observe the chart below


I have seen frustrated customers with Powerstroke 6.7L and Duramax LML trucks with high pressure fuel issues. It is to the

point that many are retrofitting the CP4 injection pump to the older CP3. The CP3 has been used on earlier diesel engines

and proven to be reliable. The CP4 does provide higher volume over the CP3 and can sustain pressures over 27,000 PSI

continuously over the CP3. We can argue over the pressures but CP4 has been used with Piezo Electric fuel injectors. CP3

injection pumps were not used with the Piezo but with solenoid equipped fuel injectors. 

                                              I have been teaching for years on common rail and have stressed that the main issue that can cause premature high- 

                                              pressure common rail fault is contamination. Manufacturers like Ford have enhanced their fuel filters and micron ratings

                                              while GM is still using, as of 2017 model year, the spin on fuel filter rated at 4 microns. Maintenance has been the issue

                                              in replacing these filters periodically due to  issue with the quality and lubricity of fuel.

​                                              Ford Power stroke 6.7L, has been using a lift pump that can easily exceed over 120 psi while GM continues to use the

                                              lift pump on the back of the CP4 injection pump. As diagnostic technicians, we see that that any air leak in GM applications (Duramax) will cause a loss or partial loss of suction which will affect dramatically the CP4 pump.  Fuel is used to lubricate the injection pumps. Loss of pressure and volume of fuel can cause air to be pressurized in the crankcase of the pump and have pistons in it to twist and have the roller assembly destroy the cam within it, In turn, metal will be generated and contaminate the whole common rail injection system. This consists of the CP4 injection pump, rails, and injectors. 

​                                                    As technicians we will see these trucks come in with no start condition and find that the truck builds no rail

                                                    pressure. You will find poor suction on a Duramax or low volume or pressure in a Power stroke 6.7L. Low high rail

                                                    pressure codes maybe set and low lift pump pressure codes may be set on the Ford 6.7L. The most important test

                                                    you need to check is for contamination. The Powerstroke 6.7L has the pressure control solenoid on the back of the

                                                    driver’s side fuel rail. The GM LML Duramax will have it in the front of the driver’s side fuel rail. You remove it and

                                                    have someone crank the engine and confirm there is no contamination especially check for metal. If there is

                                                    contamination the whole fuel system will need to be replaced. This includes the rails, injection pump, all fuel injectors and pressure [A close up of an engine Description automatically generated] control valve and volume control valve. It sounds very expensive and it is. But the issue to ask is what caused this catastrophic failure. Lift pump issues on a Ford

or loss of prime or aeration on a Duramax can be the cause. What about the condition of the fuel filters?  

Our policy on a Duramax LML or LGH is too sell the customer an aftermarket lift pump after the repair and

replacement of the injection pump and injectors. This ensures pressure and volume of fuel to the CP4 pump.

I cannot stress enough the fuel filter maintenance. There is an array of aftermarket filters available that are

as good if not better. On a Powerstroke 6.7L, we like to perform a fuel volume test at the outlet of the

secondary fuel filter in the engine compartment. We like to see a minimum volume of 1 liter in 30 seconds.

The low fuel pressure sensor will aid you if there is a drop in lift pump pressure.