Tech Talk with Tyler Robertson

I get a lot of questions, phone calls, and comments about datalinks and on board vehicle communications and diagnostics (OBD16). This article will help you, the customer, understand these data links and why DTNA uses them.

For many years DTNA vehicles were very simple, with minimal datalinks to worry about. It started out with a simple J1587/1708 datalink that came with electronic engines that allowed us to generate and read fault codes. This datalink was very slow at 9.6 kilobits per second (kps). Data packets have a certain size and are measured in “bytes”; 9.6kps is the speed those data packets travel. When ABS became mandatory on vehicles, ABS utilized this same J1587/1708 datalink. It just had to generate faults within itself, talk to the engine, and allow off board diagnostics to read it (code reader), and 9.6kps was fast enough for this application. Once the automated shift transmission was introduced 9.6kps became too slow for the engine ECU and the transmission ECU (TCU) to communicate and make shifts while matching engine and road speed. For a very brief time the J1922 was used (less than 2 years) and then the J1939 protocol came into the market. This was an industry wide datalink that travels at 256kps, and is still used today. This “high speed” datalink allowed the engine, transmission, ABS, and now the instrument cluster unit (ICU) to all communicate at a rate of speed that was compatible for all ECUs.

The J1939 has been the standard datalink protocol since the late 1990’s, as well as the J1587/1708. It has been wired directly to the diagnostic connector on the vehicle and easily read by off board diagnostic tools and aftermarket readers. When Mercedes Benz heavy duty engines (MBE) entered the North American Market we were introduced to a (2 box) engine ECU, a DDEC-ECU and a DDEC-VCU. The J1587/1708 and J1939 communicated to the VCU mounted in the cab, and the VCU talked to the ECU over a proprietary controller area network (CAN) link. At first this only needed about 125kps, but was NOT intended to be “tapped into”. As EPA levels increased the need for data transfer speed increased, to what we use today on the PT-CAN (powertrain CAN) at 667kps. Some models of DTNA vehicles will also use a “cabin CAN” (Cascadia) which allow vehicle and chassis side modules to communicate again at a low speed of 128kps, but also communicate to the engine ECU’s via the 256kps J1339 and the slow J1587/1708.

Why does this mean anything to you, the customer that just purchased a new Western Star, or other DTNA vehicle? Today, and for the last few years, transport companies have been pushing satellite tracking devices and “e-logs”. These systems require a connection to the engine ECU to monitor road speed, fuel mileage, time in cruise control, and many other things. To do this they could add a branch to the J1939 by plugging into the splice pack provided by the factory, OR some have created a “Y” connection harness that plugs into the diagnostic connector, which is a direct link to the J1939.

As of January 4th 2016, things changed on all DTNA vehicles, including your new Western Star. The introduction to OBD16 enters the picture with GHG17 compliant vehicles. “How do I know if I have a vehicle with OBD16?” If your 9 pin diagnostic connector is GREEN in color, you have an OBD16 vehicle and this is how it affects you.

Pre OBD16 connector


OBD16 connector


The EPA mandated closer monitoring of the engine operation and emission system. It not only had to be compliant leaving the factory, but be compliant over its
lifetime. This required a system that had to be self-diagnosing and self-monitoring. This is where the “high speed J1939” comes into play. This datalink has a few industry terms, such as “H1939” and “J1939 CAN”. This data link travels at twice the speed of the old J1939 at 500kps. This is the datalink in your green diagnostic connector. DTNA has also removed the J1587/1708. The satellite system your company wants to install still travels on the 256kps J1939, as well as some other aftermarket products. DTNA still installs that datalink so it is available to aftermarket tracking systems. It just HAS to be tapped into from one of the three splice packs in the dash (see example below) If it is done any other way the vehicle will have communication issues. It could result in check engine lights and possible shut down of the unit. In part 2 of Datalinks next month I will discuss the importance of not cutting, soldering or improperly “tapping”, and how to diagnose a datalink problem and make a proper repair. Think of it this way, imagine you are driving down a highway at 100 km/h, like a data pack traveling on the H1939 at 500kps. Then you come up to a vehicle traveling at 50 km/h, like a data pack traveling at 256kps. Information traffic gets blocked and is “late” getting to where it needs to be, and usually becomes corrupted. If you are looking to order a new Western Star, ask sales about the optional “black 9 pin connector”. This connector is tied up and tucked away under the dash and only accessible by removing cover panels, It will allow the satellite tracking system to use the “Y” connector harness to communicate to the data link on the 256kps J1939. This is OPTIONAL and has to be requested upon order of the truck.

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Hopefully this clarifies DTNA vehicle datalinks and helps you, the customer, understand how and why DTNA uses them. It should also give you a better understanding of how to add systems that require datalink communications to the vehicle and engine ECU. Check in monthly for other informative Tech Talk articles on questions and issues consumers are having on today’s DTNA vehicles.

Tyler Robertson, Winacott Equipment Group

Dealer Trainer and Tech Support.