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Heavy Duty: Keeping Up With Modern ABS

April 9, 2008
What your technicians need to know about troubleshooting today’s ABS.

Modern electronics and computers have dramatically cut the time it takes to troubleshoot ABS—meaning less “winging it” by your technicians—but properly maintaining the systems still seems to be another matter. Just ask Bob Blair.

The CEO of the Spokane, WA-based Lite-Check, Blair says a recent trip to a shop for a product demo convinced him some technicians still have no idea what they are doing with ABS.

“They had a trailer there where the ABS was not functioning, and they’d already spent three or four hours trying to figure it out and were at the point of replacing the ECU,” Blair says. “We plugged in the (diagnostic tool) and the first thing I did was to verify that the brake circuit and the auxiliary circuit were working, because that’s what powers the ECU. Well, when I hit the auxiliary circuit, the alarm came on—there was no power being delivered to the ECU. So the technician crawled under the front of the trailer and walked the auxiliary circuit back, and about 20 feet from the nose plug, there was an undone connection. He connected the circuit, the alarm went off, and we heard immediately the ‘click, click, click’ of the ECU.”


Unfortunately, lack of training and knowledge about ABS can end up costing the fleet far more than a new ECU. Last June, inspectors from the Commercial Vehicle Safety Alliance (CVSA) and Federal Motor Carrier Safety Administration fanned out across North America to perform 62,370 inspections on trucks and buses during Roadcheck 2007.

According to CVSA, brakes were the main issue, comprising 54 percent of total vehicle defects. A recent DOT study indicated brake problems were present at the time of a crash in nearly a third of all reported accidents.

Technicians should have had plenty of time to hone their ABS skills, as the National Highway Traffic Safety Administration (NHTSA) has for a decade required the systems on air-brake equipped truck-tractors, semi-trailers and single-unit trucks equipped with air brakes and hydraulically braked single-unit trucks over 10,000 pounds GVW.

Despite the occasional horror story from the shop, Rick Conklin, product manager with Elyria, OH-based Bendix Commercial Vehicles Systems, said many technicians have actually gone through a “pretty good” learning curve with ABS.

“The average technician out there is a lot smarter about electronic systems than five or 10 years ago,” Conklin says. “The end result is that a lot of the (problems of misdiagnoses) we saw with the first introduction of ABS and then with the mandate of ABS are really no longer problems. The parts changers have gotten word that that’s not necessarily the right thing to do, and that you do need to look into system level to be able to appropriately diagnose. And the service tools have gotten easier to use as well as the service documentation has gotten better and more clear for the technician to use on a daily basis.”

Duane Stocksdale, product manager—braking controls division with Kansas City, MO-based Haldex Brake Systems, says despite technician turnover that is creating problems for the industry, modern electronics have helped make their jobs easier.

“The ABS equipment and control modules have become more stable and there’s a lot more diagnostic tools out there,” Stocksdale says. “In the early days, everybody was trying to use blink codes and that made it more problematic, but now there’s more hand-held devices and a lot more use of PCs and diagnostic devices, where you have drop-down windows that lead you to the diagnostic area you need to take care of.”


They’re not free, but from keeping drivers and cargo safer on the road to using telematics to train drivers to avoid accidents, there are many reasons ABS is good for a fleet’s bottom line. The main thing fleets are looking for in ABS is reliability, says Stocksdale.

“Some are just interested in the minimal ABS, because legislation requires it, therefore they’ve got to pay for it,” he says. “More people are at least trying to understand the auxiliary capabilities they can get—the ABS electronic control module can drive and manage other devices on the vehicle, so they’re looking at those as operational improvements.”

Another advantage of ABS is the use of telematics, says Matt Williams, manager of fleet sales, service and training with Troy, MI-based Meritor WABCO. Information gained can help fleets save on accident costs, providing both a safer option and a better return on investment.

“If you can prevent (an accident), that means the cargo’s going to get their safely,” he says. “It all depends on the fleet’s needs.”

Bendix electronic marketing manager Fred Andersky says fleets now want instant information on ABS interventions and issues.

“You’ll eventually reach a point where the service shop will get a message from the truck that indicates, say, a wheel speed sensor is acting up, and by the time the truck gets into that service shop, they’ve already got the wheel speed sensor, the fault code, they know what they need to get in there and do and they’re able to do it and get the driver back out on the road as quickly as possible,” he says.


Mark Hadley, director of fleet maintenance and property with the West Valley City, UT-based Central Refrigerated, has seen the evolution of ABS, and is glad his 1,850 Class-8 trucks have modern systems from Bendix.

“We make it mandatory that if an ABS light comes on, they get it fixed, because there is value in that ABS system,” he says. “You don’t see trucks any more that veer off and jackknife from a hard brake; they pretty much go straight down the road. The systems have been mostly flawless—very few codes, very few breakdowns related to that technology.”

Modern electronics, computers and software programs have made it much easier for technicians to troubleshoot ABS, but Hadley says even the best systems are not much use if the technicians don’t know how to maintain the systems.

“Obviously, they have to have the computer skills to be able to understand what the information is telling them,” he says. “On the technical side, they need to know how to download and interpret the data and follow the troubleshooting codes. They have simplified it enough; they have a troubleshooting tree to be able to tell you what the codes are telling you. That’s how you get your people trained. Just hook up the computer and it will walk you right through it, rather than try to troubleshoot and think you know it.”

In fact, Hadley says there is no such thing as too much training for his technicians, especially when there is a learning curve involved, as with modern electronics. He says going the extra mile to keep technicians up on the latest techniques and technology ends up being a big money-saver.

“When you’re as big as we are, manufacturers are offering training and we take advantage of all of it,” Hadley says. “Then it’s keeping it updated, (because) there’s always something new, and you have to make sure you have the latest enhancements. The technicians get paid for the time they spend on the equipment, so it’s important that they shorten their troubleshooting time by using that computer.”


Today’s ABS are by no means simple pieces of machinery. They generally include wheel speed sensing equipment, an electronic control unit (ECU), brake pressure modulator valves and a variety of electrical harnesses, switches, relays and lamps to interface with the vehicle power train, electrical and braking systems.

Sensors monitor wheel speed and relay information to the ECU, which sends signals to the modulator valve to provide the needed amount of brake pressure, determines if a wheel is about to lock up and activates the ABS valves, which regulate air pressure to the brake chambers, preventing a lock-up.

Despite all the gadgetry, Williams said the first step in properly troubleshooting and maintaining ABS is knowing basic electrical principles like ohms and voltage, and knowing how to use a voltmeter.

“(Technicians need to know) not only those specifics, but how the systems work as a whole—theoretically speaking, how the ABS monitors wheel speed, how it’s looking at wheel speed and how it reacts during certain vehicle maneuvers is also a key that a lot of technicians really need to know when they’re working on a system,” he says.”

The basics are still just as important though—when installing or removing the systems, Williams says technicians should make sure they stick to proper procedures.

“Be careful where they tie-strap a connector or a wiring harness,” he says. “That is very important.”

Bendix’s Conklin says their system will announce the need for maintenance, giving technicians one less thing to worry about.

“Of course, a driver with good pre-trip inspections and periodic vehicle inspections is always a good practice, but the system keeps pretty good tabs on its relative health and the diagnostic tools available make it fairly simple to diagnose and service,” he says. “We don’t get a lot of calls we don’t understand, because the tools have reached a maturity and also the technicians have reached a maturity where they’ve got it.”

Good preventative maintenance practices are still important, though.

“These don’t take away the responsibility for keeping an eye on things and keeping things in adjustment and checking things out ahead of time,” Andersky says.

Stocksdale says most ABS problems are related to the power source or wheel speed sensor.

“Anytime you’re maintaining the wheel end or an initial installation, make sure you have a good, solid installation; the sensor pushed up against the exciter ring and again, dialectic grease at any connecting point,” he says.


Today’s ABS can help keep your trucks moving safely down the road, and fleets have plenty of good options to meet their needs, but ultimately how well they work depends on you and your technicians.

While modern electronics have certainly made it less time-consuming to properly maintain anti-lock braking systems, it takes no less dedication to making sure none of your technicians takes a shortcut in the shop that could lead to disaster on the highway.

The trick is getting your technicians to buy into the fact that while checking the brakes might now take a lot less of their workday, they can’t give it short shrift.

Do that, and ABS will help keep your fleet safely and efficiently moving forward.


Bob Blair, CEO of Lite-Check said the company’s “910B” inspector is a necessary tool for technicians that maintain ABS.

Blair says the advantage of their tool is that it can test a vehicle’s air, brake and electrical systems, which are all connected to ABS.

“So on the electrical (side), for example, if the software in the tester discovers a circuit fault it will automatically sound an alarm and tell you what the fault is,” Blair says. “So the technician can be at the rear of the trailer, 50-70 feet away from the tester, press a button like a brake circuit, and he hears the alarm and he can see that the lights are not operating correctly and now he knows he’s got a problem. The moment he corrects that, the alarm (shuts) off.”

The goal, Blair says, is reducing the time needed for technicians to diagnose ABS problems, leaving them more time to make repairs.

“TMC conducted a survey and determined than 30-35 percent of a technician’s time was spent diagnosing, not fixing, so we’ve approached it from the standpoint, ‘Can we get that information to the technician within a second?’” he says. “And now you’re getting a good population of vehicles out there with ABS on it, and (fleet officials) are also starting to realize the time required to diagnose the problems. (Also), when the technician is on the service truck, he now only needs this one tool and when he connects with the seven-way (plug), he can read ABS and electrical at the same time.”

Well-maintained fleet vehicles’ ABS should be checked after every major cross-country run or every 30 days, Blair says, so being able to make a quick check is important.

“The advantages of not having road costs and violations and all that kind of things are incredible,” he says. “When the tester can identify what the problem is with that sensor within a fraction of a second, how much help is that for the person working in the rain?”

The tester comes with manual and a “cheat sheet,” but Blair says they are rarely needed.

“We rarely get a call on how to use it,” he says. “You connect the seven-way and the two airlines, press the ABS key and it will automatically search and identify which type of system is on the trailer and automatically pull up the first fault on the screen. If the technician is not familiar with that fault, he hits another button and it will scroll through a help process—‘Check this, measure this,’ whatever, so he doesn’t need a manual.”

About the Author

Fleet Maintenance staff

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