What is J1939 protocol, and why should you care?

When looking at different engines, you may encounter the term J1939, and this term is important, but why?

J1939 is the proprietary name of the protocol used by engine manufacturers for vehicles. Much like spoken languages, such as Chinese or English, J1939 Protocol refers to the language that the engine “speaks”. The ECU of the engine takes the signals sent by the engine sensors and either makes adjustments (as in fuel to air mixture) or communicates that information, either to a display, or to a software program.

Much like language in humans requires listening and speaking, an engine protocol requires both receiving information and communicating that information. So, what is J1939. J1939 is the SAE standard that engine manufacturers typically use to ensure that the engine is in compliance with industry standards. Since the majority of marine engines are derived from automobile, truck, or other engines, this protocol is largely standard. Additionally, there are various ISO standards that are also required, often mandated by law. However, J1939 is not mandated. It has simply become the overall standard that most engine makers use.

Why is this? In short, nothing legally requires an engine maker to use the J1939 protocol, but should an engine maker not use J1939, they would face major problems with component compatibility (like ECUs), monitoring systems, and even from manufacturers of gauges. Additionally, since the maintenance shops at marinas, government, and commercial operators are equipped to deal with J1939, end user maintenance becomes much easier and cheaper when standards are in place. Does Marinediesel comply?

Like most manufacturers, Marinediesel uses J1939 in the programming on our ECU. J1939 is an incredibly flexible protocol, and there are differences between J1939 for off road and on road use. However, most engine monitoring systems should be able to communicate with our engines, not only with fault codes, but in monitoring performance. Additionally, aftermarket vessel systems that require engine data (such as fuel management systems) should be compatible with Marinediesel engines.

Need to contact Marinediesel for technical assistance? We need your engine serial number.

Though we recently posted this question in our   Engine Maintenance FAQ, this subject is really important, so we will occasionally post reminders about it on the blog.

Why are we making a big deal out of the engine serial number?

Quite simply, because the engines are continually evolving and changing from one year to the next. As an example, there have been about ten versions of the Marinediesel VGT Series. As engines progress from idea, to development, to testing, to market introduction, to production, different components are either tweaked or changed based on field experience and feedback from our customers.

In a way, it is very similar to the updates that computer software publishers make as bugs are discovered. Indeed, given the electronic nature of the VGT Series and the use of the NIRA ECU, software updates are often one of the changes we make.

When an engine is manufactured, detailed production notes are kept about that specific engine during the production process. We know, for example, which turbocharger was equipped on the engine, what software version was installed, and custom configuration, etc.

Additionally, the engine serial number allows us to see any changes made to an engine, by Marinediesel, since that engine was sold. Indeed, we recently has a mechanical issue with a customer where there were changes made to the engine, and nobody (including our customer!) could remember what was specifically done to the engine. Our technical team having the serial number eliminates problems and issues like that.

So, before contacting Marinediesel with technical questions, you should look up the engine’s serial number first, so we can give you an accurate solution for your engine problem.


Location of engine serial number, VGT Series


Who is NIRA?


MarineDiesel’s VGT Series of marine engines goes against the Bosch mold in the industry when it comes to the electronics and ECU with which the engine is equipped. Why?

The simple answer is that there are other control units on the market that are more adaptable, more reliable, and offer far more flexibility. We use a NIRA ECU with our VGT engines, and we do so because this ECU lets us “customize”, to customer requirements, the performance of the engine. We can program multiple engine MAPs into the ECU, and it allows an operator to change, via a switch, how the engine performs (ie: on a military boat, one MAP for patrol and a different MAP for boarding.

Who is NIRA?

NIRA is NIRA Dynamics AB, a Swedish company that specializes in monitoring and electronic control systems.

From the NIRA Website

A Swedish expert company focusing on innovative software solutions for vehicles

NIRA Dynamics was founded in 2001 and is located in Mjärdevi Science Park in Linköping, Sweden, from where we support customers and partners worldwide.


NIRA Dynamics is developing unique sensor fusion based systems for different vehicle applications that utilize the potential in the sensor fusion idea to improve the performance, reduce the system cost and at the same time, increase the customer value. Through close collaborations with world-class research groups at Linköpings universitet, Sweden, and Chalmers University of Technology, Sweden, NIRA Dynamics is constantly in touch with the research frontier in these and other areas where sensor fusion and other types of signal processing are employed.

Sensor Fusion

Sensor fusion, or sensor data fusion, can be described as using information from several different physical sensors to compute new, virtual sensor signals. The virtual sensors can in principle be of two different types:

  • Improved versions of physical sensor signals, or
  • So-called ‘soft sensors’ or virtual sensors that have no direct physical counterpart.

In both cases sensor fusion adds value, not cost.


By using technologically advanced components produced by companies such as NIRA, MarineDiesel ensures that our customers get the high levels of performance that they require.



What is Common Rail?



If you read the marketing material put out by MarineDiesel or other engine manufacturers, you are likely to encounter the term “common rail” when the engines are described.

What exactly does common rail mean?

First off, all Marinediesel engines are common rail engines. There are a number of reasons behind this design, but mostly related to both efficiency and the need to comply with emissions regulations.

Common rail engines feature a fuel injection system that features all injectors connected along a single, high pressure (up to 30,000 psi) fuel line, controlled by the engine’s electronic system (ECU).

Older engines had the injectors fed individually at a continuous rate via a cam and though the timing was precise, it was not variable.

The electronic control of fuel supply and pressure provides better atomization of the fuel for combustion, resulting in lower emissions, reduced noise, and optimized engine efficiency with reduced fuel consumption.

Hence the virtual requirement for modern diesel engines to be designed using common rail fuel systems.

Of course, the drawback to common rail engines is that these increased pressures require extra vigilance in maintaining the maintenance schedules as required in your engine’s manual (whether for a MarineDiesel engine or the engine of any other manufacturer).



Maintenance Tip of the Week – Dongle 10/20/2014


Maintenance Tip of the Week:

Be extremely careful with the dongle on the ECU software. They can be easily damaged or lost, and you cannot access the software without them. They are also relatively expensive to replace, since they are effectively your software “license”.



Maintenance Tip of the Week – ECU 09/29/2014



Maintenance Tip of the Week:

MarineDiesel’s 6.6L VGT range of engines are electronic. In properly maintaining and diagnosing engine problems, the software is a must. It is available, along with the connecting cable, when you purchase the engine.

Here’s why…

Electronic engines are complex, meet modern emissions and fuel standards, and use thousands of sensor inputs to maintain the proper fuel to air mixture for combustion: Far greater amounts of data than can be gleaned from simple analog gauges. A single sensor failure can be difficult to locate without software, and a misdiagnosis can become very expensive, very quickly. Every engine maker uses their own ECU to collect this data and control the engine. Though the MarineDiesel engines use SAE J-1939 data as the standard, and, in theory, could work on other electronic engines using the same protocol, the software is intended specifically for MarineDiesel engines and should not be used with other engines. Other manufacturers may use more, or fewer, data points, and their fault codes will also be different, even if the sensor’s data is the same.






ECU, Dongle, and NIRA



nira screen

As we have written on this blog before, our VGT Series of engines uses a NIRA ECU to both report faults and control the engine functions.

A primary reason we use NIRA is that it is easily accessed by MarineDiesel technicians in addition to being programmable.

So, you buy a VGT engine from us. How do you access the engine data?

It is really simple. You need:

  • MD diagnostic software
  • A laptop
  • A connecting cable
  • A dongle



Training on how to use the software.

We don’t charge anything for the software. Nearly every shop nowadays has laptops available for technicians. Cables are cheap.

What we charge for is the dongles, and there are many reasons we do so:

Most importantly, we need to restrict who has access to your engine’s functions. The NIRA software is not very difficult to learn, but it can be unforgiving. Untrained people making changes can easily ruin your engine. The average user or boat owner will not be able to learn this software without training (It is NOT intuitive). Therefore, in order to forestall problems, we charge for the dongles.

Our engines are often used on boats, surrounded by water. Ever drop your keys, or sunglasses, in the drink?

The dongle grants access to licensed software. The software is freely available, and uses international standards, but it is the intellectual property of NIRA nonetheless.

All of our dealers carry multiple dongles for their technicians to use. They usually purchase these when they undergo our training program. Some large customers undergo extensive training, and they, too, carry these in inventory. However, though an ECU is software, it was not necessarily ever intended to be modified by the average Joe.


What is an ECU and what does it do?



MarineDiesel’s VGT Series of engines are all electronic. That means that they are controlled by an ECU.

What is the ECU and how does it function?

Quite simply, ECU stands for “Engine Control Unit”, and, at its’ simplest definition, controls the air to fuel ratio in the engine, therefore controlling combustion. However, the ECU also does much more than this. It is the interface between engine, vessel, engineer, and manufacturer. It is the heart of the entire vessel electronic system. It is also the one component that the engine simply cannot operate without.

Wikipedia has a pretty good explanation HERE for more detail.

In the marine engine market, there are two primary manufacturers who make ECUs for 95% of the worldwide market:




Though MarineDiesel has, in the past, used Bosch ECUs, and continues to use them on some custom or industrial engine applications, our entire VGT Series of engines uses the NIRA ECU… and here’s why:

The NIRA ECU is customizable, and programmable. Through the NIRA software interface, we can monitor thousands of sensors and data  points on every engine installed. Effectively, we can force the engine to behave in a certain way, as defined by the customer, by programming multiple engine MAPS into the ECU, changing the performance as required. This functionality becomes particularly important in military operations where vessel may be required to perform multiple types of missions.

The Bosch ECUs, though reliable, are neither programmable, nor are they customizable easily (unless large volumes are purchased on a project, in which case the customization gets very expensive).

Through the NIRA software, MarineDiesel, our dealers, or customers can easily “plug in” to the engine and obtain instant diagnostic information, requiring only a laptop, cable, and connector.




Ask Professor Diesel – 06/16/2014


This week’s question comes from Mike in Australia:

Professor Diesel:

My VGT engine is electronic, so that means I should be able to perform diagnostics on the engine myself, correct? Can I buy something to receive this information, or must I go through a dealer for service.



Mike, the engine’s ECU is accessed through a special connector that we can provide and read by using software on your laptop or tablet. The ECU unit itself is set to customer specifications at the factory and is maintenance free.

Please note that we are often hesitant to sell this item to individual customers for several good reasons:

It requires training to understand the output and fault codes.

The ECU that we use is programmable. Entering information into the ECU can seriously damage the engine or hamper performance if done improperly. This software is not Angry Birds… it is not intuitive to learn, and if you make a mistake, it is often expensive to fix (no simple log in and get another “life”).

Dealers use this software as a diagnostic tool only, on site, so they can quickly diagnose and repair engine problems. It is usually best to leave the ECU to them.

If you have a question you would like to have answered, simply submit it in the form below:

[accua-form fid=”9″]




Derating – What does it mean?



Engine buyers are often presented, as a sales pitch, with a lot of gobbledygook about horsepower, torque, how great an engine performs, and so on…

How much is actually true?

With MarineDiesel, you get what you pay for. If you buy 500 hp, you get 500 hp.

Nothing is as frustrating to a vessel operator as receiving a new vessel and finding out that the engines are not producing the power that they thought they had purchased.

Why do these scenarios happen?

It is related to derating.

Engines can be either intentionally derated or unintentionally derated.

Intentional derating occurs when the customer asks the manufacturer to change the engine rating to alter performance or life cycle. There are many reasons why someone would want to do this. Every vessel is designed for a specific purpose and sometimes the vessel’s mission does not neatly fit into a range of standard options or offerings. For instance, if an operator wants a longer service life on the engine, and is willing to accept a reduction in power to receive that service life, the engine can be configured to provide that requirement.

Unintentional derating is a much more troubling scenario. When engines are rated, they are “certified” to provide a certain amount of power and torque for a specific period of time in a specific set of conditions. This is the fine print in the engine brochures and advertising that is usually not very prominent, or is sometimes even missing entirely.

Engines require adequate cooling in order to function properly. If an engine is rated at one level with ambient air temperature of 25 deg. C, using a specific fuel, what would happen if that engine was operating in an environment with an ambient air temperature of 40 deg. C?

The engine will not provide the same amount of power. It must work harder, and the result is a loss.

This is the frustration of the customer. He goes to an engine dealer, is assured of a specific level of power, yet received something else.

This is an area where MarineDiesel shines. Our VGT Series of engines features our own, programmable ECU. We can rate the engines according to climate, use, or customer specifications.

Since the majority of our sales are to military users, who normally must operate in a wide range of temperature extremes, our standard engine ratings assume far harsher conditions than the average customer is likely to experience. If that customer requires something different, it can usually be delivered quickly, and cheaply.

Some specific information about the VGT Series ratings:

Power Standards

The engine performance corresponds to ISO 3046 and a fuel with specific calorific value of 42,7 MJ/kg (18 360 BTU/lb) and a density of 0,84 kg/litre (7.01 lb/US gal, 8.42 lb/Imp gal).

The engines will operate up to 1000 m altitude and 40°C without derating. For operation at higher altitudes the power will be derated according to the following factors:
Altitude derating factor up to 3000 m 4% / 500 m
Altitude derating factor over 3000 m 6% / 500 m
Ambient temperature derating factor* 2% / 5°C
Humidity No derating
*Ambient air temperature at aircleaner inlet