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It’s Electrifying

Discussions about the latest round of emissions regulations have tended to focus on the debate over the use of Diesel Exhaust Fluid (DEF), but several changes to vehicle electrical systems are also coming along for the ride.This year, the...


Discussions about the latest round of emissions regulations have tended to focus on the debate over the use of Diesel Exhaust Fluid (DEF), but several changes to vehicle electrical systems are also coming along for the ride.

This year, the lead engine family offered by every manufacturer will need to meet new rules for Heavy-Duty On-Board Diagnostics (HDOBD), which will carefully watch over the emission-controlling equipment. All new engines will incorporate the related capabilities by 2014.

The vehicle will monitor itself and problems with the system will be captured for anyone who downloads OBD data, says Mark Kachmarsky of Volvo and Mack Trucks. New threshold monitors will detect failures that cause emissions to exceed allowable limits, functional monitors will determine if an issue is indeed a failure, and component monitors will determine if sensors are working in the proper range.

A fault picked up by the Engine Control Module will also be broadcast over the vehicle’s communication network, activating new Malfunction Indicator Lights in the dashboard.

“The instrument clusters are changing a little,” notes Paul Menig, chief engineer of mechatronics engineering with Daimler Trucks North America. For drivers, that will mean some new ISO-approved symbols in the instrument panel to watch over the activities of emission controls, indicator lights associated with the regeneration of Diesel Particulate Filters, and even text messages in selected cases.

Quite simply, more information is being collected and displayed than ever before.

But the electrical changes are not limited to OBD alone. Updates will support another Aftertreatment Control Module, Diesel Exhaust Fluid injector, sensors to monitor levels of the fluid, and supply line heaters, says Kachmarsky. “They’re all talking. They’re all harmonizing the performance of the vehicle,” he adds, referring to the way the systems are interacting. For example, temperatures need to reach a certain point before the Diesel Exhaust Fluid can even be applied.

“The look and feel [of diagnostics] is about the same, but there are some new features with some extra panels coming on,” Menig adds, noting how the new systems will measure the amount of DEF that is used.

Combined, all the capabilities have led to widespread changes in the look of an electrical harness.

“Look at how much fuel you need because it is tight on the chassis,” says Menig, referring to the DEF tank with its sensors and heater, four new sensors to monitor the SCR process, and three new sensors on the DEF metering unit, whether it is assisted pneumatically or electrically. Then add a couple of new computers in the mix.

Front axle locations and cab height can affect where different pieces are attached. The DEF, for example, might be on one side of the fuel tank or the other, and that is going to affect the wiring harness, Menig says. “The first challenge you’re going to have is determining where everything is.

“Pay attention to your manufacturer and your engine manufacturer to help you understand what you’re going to see on the vehicle,” he adds. “We’ve all done an excellent job to help routing and clipping. If you remove something while servicing, please put it back.”

The electrical upgrades are not limited to engines that will use the new fluid.

“Our main changes are on the engine harness,” says John Jacob, electrical components manager at Navistar, referring to the Heavy-Duty On-Board Diagnostics. New aftertreatment fuel dosers incorporate temperature and pressure sensors, and there is a boost control for the series turbo in addition to humidity sensors.

The changes that have emerged have made it more important than ever for mechanics to watch for alterations to the electrical systems.

Menig, for example, refers to a new Power Net Distribution Box that includes all the fuses. “This also becomes the load disconnect switch,” he says. “No longer do I have to have the mechanical switch and electrical switch that can be its own problem… now it is a plastic electrically-controlled switch that is driving a large relay.

“Grounding is important as well to make sure you’re going to get the best opportunity to get all these computers working properly,” he adds, referring to a solid copper wire going to the starter and the redundant use of the chassis.

Kachmarsky, meanwhile, referred to one truism that will apply to every shop.

“Service tools are a must,” he said. “The training on these tools should be considered mandatory in any service facility or garage.”MT


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