Medium Duty: Body, Say ‘Hi’ to Chassis

How many times have you seen a science-fiction movie where the hero can miraculously communicate with an alien life form because he’s brought along his trusty “universal translator?” How cool would it be to have that in real life?

Okay, maybe that’s far-fetched, but the vocational truck industry may soon have something like that, in the form of the Technology & Maintenance Council (TMC) Recommended Practice (RP) 1507: Recommendations for a J1939 Network Interface Strategy. According to TMC, the purpose of RP 1507 is “…to recommend key elements of a J1939 network interface strategy for use by vocational/specialty vehicle OEMs.”

“The current PR is a first step,” says Cindy Florek, who chaired the RP 1507 Task Force for TMC. “Not all the issues of J1939 implementation are addressed in this RP.”

A senior project engineer with Allison Transmission, Florek is well-versed in J1939 communications, and the need to get body builders talking to chassis OEMs. And, after serving as Task Force Chair, she is equally well-versed in the challenges of getting both chassis OEMs and body builders to the table. “We attempted to address a common OEM and installed body builder connector and connector location recommendation and could not get consensus,” she says. “We also attempted to engage body builders in the development of this RP. We wanted to understand what J1939 messages they are currently using and what messages they would need to have identified by the SAE J1939 committee.”

Fortunately, several fleets were more than happy to participate in the Task Force, and let the manufacturers know what they wanted and needed in a communications standard. “Fleets were primarily interested in making sure they get a reliable network system that can be tailored to their needs,” Florek says. “The network troubleshooting and repairing should happen without having engineers from OEMs, suppliers, and body builders in the service bays.”


The J1939 standard came about because chassis OEMs and body builders were trying to address cost and reliability, according Bob McClure, co-founder of telematics company, and a RP 1507 Task Force member. “One of the advantages of J1939 is that you can use it to do multiplexing,” he explains. “And as such, that allows you to cut the cost of copper—you get rid of a lot of wires, and copper is extremely expensive. For example, I can buy a computer chip cheaper than I can buy a connector. A good connector will run you $3 to $50; a computer chip will run you $3 to $20.”

According to McClure, wiring is and always has been a truck-building nightmare. “You’ve got all those wires and the cost of a wiring harness is unbelievably expensive,” he says. “And from a maintenance standpoint, when one of those wires or one of those bundles breaks, or has a bad connection, it can literally take you days if not weeks to find an intermittent connection.”

Multiplexing replaces all the wires in a traditional harness with only two wires running the entire length of the truck. Costs are reduced, maintenance is simplified and diagnostic capabilities are increased. “From a build point of view, the cost drops dramatically, because you get rid of all those wires and connectors,” McClure says. “And from a maintenance point of view, you have the advantage of having distributed processing, so I can have the processor run diagnostics on itself and power up and tell whether it’s got an intermittent connection, and if so, where. I can have the computer tell me which one of those wires is getting flaky on me.”


McClure credits engine, transmission, and brake manufacturers for pushing J1939 as a way to get a communications technology in place where they could fully integrate a vehicle’s driveline.

“If you have a car that’s built in 1995 or later, with anti-lock brakes, and the engine and the brakes and the transmission are all talking together, you’ve got a truly integrated vehicle,” he explains. “You know that the transmission, the brakes and the engine are all working together. If you step on the brakes, the transmission, engine and brakes will all decide how hard to brake you safely. People today just don’t worry about skidding like they used to.”

For a long time, however, truck and bus operators couldn’t take advantage of this technology. Heavy duty engine, transmission and brake manufacturers simply didn’t have common language.

“That’s how J1939 came to be,” says McClure. “This is how (these components will) talk together. The whole goal was to get an integrated truck to meet the safety requirements of the Federal Motor Carriers Safety Administration and the emissions requirements of the EPA.”

Today that goal has been reached, and a heavy vehicle of today using J1939 is very different from a heavy vehicle of ten years ago. A former Allison man, McClure naturally uses an example from his days with the transmission manufacturer: “Their transmission will actually control the torque of the engine during the shift,” he says. “So that on a passenger bus, there used to be a jerk there and if you had a passenger standing up it might knock them down. They will not feel that shift today.”


The problem faced by the RP 1507 Task Force, McClure explains, is that not everyone adheres to J1939. Body builders for vocational trucks don’t understand the protocol, he says, and so they don’t use it, even when told that it can cut costs and increase reliability.

The fleets get it. Why don’t the body builders?

“It (J1939) has cut the fleets’ time for repair immensely, because they get their PC, they roll it out there, and it does a lot of automated diagnostics for them,” McClure says. “If they can start going to the body builders and saying, ‘You see the kind of test integration we have over here for diagnostics and troubleshooting? Why can’t we have that across the entire vehicle? What can you do to give us those services?’ that’s going to lead to maintenance costs going down, and sales going up.


Will RP 1507 lead to better integration between chassis builder and body builder? It must, according to Mike Ehrenhaft, manager of technical maintenance—chassis for Waste Management, Inc, and another RP 1507 Task Force member.

“I’m coming at this specifically from the refuse application, but there have always been communications issues that exist between the first stage manufacturer—the OEM—and the second stage manufacturer—the body company,” he says. “When these two don’t talk, out jumps the devil.”

The problem, as Ehrenhaft sees it, is that the OEMs and body builders are constantly improving their products, to grow with the needs of the customers and remain competitive —a good thing—but, for a variety of reasons, they do their product development in a vacuum—not always a good thing. “So, they might develop an idea, but they keep it internal until it’s time to implement it in production,” he explains.

“If these changes aren’t communicated between the chassis OEM and the body OEM, there are interface problems,” Ehrenhaft says. “And either one of them can be guilty: the chassis manufacturer, the first stage, can evolve their electronics and not let the body companies know, hoping they’ll catch on, and the body company can do the same. The bottom line is, one company’s success can cause a problem for another company to solve.”


But companies can’t be counted on to solve each others’ problems, and that’s where RP 1507 comes in. Two major objectives were for the establishment of a standard connector between chassis and body, and a standard location for that connector on the chassis.

“We wanted to provide a standard location for a plug, or connection, that would connect the chassis to the second stage, or body,” Ehrenhaft says. “We spent several days trying to determine where, on a particular type of chassis—either conventional or cab-over—to put it. Should we be back of the cab? Should we be a firewall location? Should we be left or right? How high? What’s the design of the plug? As inconsequential as those things sound, they are significant when the manufacturer has to source the components and build them into the truck plants.”

Of course, fleets like Waste Management can tell the manufacturers what they want, but there’s no guarantee that the manufacturers will listen. “We, as a customer, say there are certain things we’d like to see geared towards J1939, and the manufacturers will in some cases agree, or will push back, because of the level of difficulty implementing it into production,” Ehrenhaft says.

“The downside to this is that it’s too early to tell how well these issues have been addressed,” he continues. “Because it’s an RP, it stands for ‘Recommended Practice,’ and the OEMs don’t have to comply. We think it’s in everyone’s best interest, and the OEMs in attendance think the same, but when they move to their new product development teams and their product planning groups, their sourcing people, they may not have the same level of enthusiasm as we did in the Task Force. So we’re hoping that both the first-stage and final-stage manufacturers will really grab onto and embrace this RP.”


If and when they do, the impact on vocational fleets could be enormous. Ehrenhaft looks forward to quicker delivery time on ordered vehicles, better quality of those delivered vehicles, a more consistent product, and something even more important: “Probably one of the biggest things for the vocational side—and maybe the over-the-road side as well—is, hopefully, a reduction in finger-pointing,’ he says. “If everyone is singing from the same hymnal, the process runs very smoothly.”

When that day comes, and everyone is singing from the hymnal called RP 1507, fleets will be able to trace problems directly to their source. As Ehrenhaft puts it, the RP 1507 standard connector joining chassis electronics to body electronics will enable technicians to say ‘This problem begins and ends at this connection.’ “If it’s from this point forward, it’s yours, first-stage manufacturer,” he explains. “And if it’s from here rearward, it’s the second, or final-stage manufacturer’s.”

Is RP 1507 the “universal translator” that will enable chassis and bodies to talk to each other (and include maintenance technicians in the conversation as well)? A lot depends on whether the body builders are even listening. Cindy Florek notes that she sent invitations to a few hundred body builders to participate in the RP 1507 Task Force, but got “very little interest.”