ABS Troubleshooting: Is There Still A Problem?

Why are technicians still misdiagnosing ABS?

Reid points out that the information on how to properly set the sensor was readily available to the technician in Bendix's product documentation, training CDs and videos.


The experts agree that as brake systems become more complex, technicians will need to develop their diagnostic skills to keep up.

Today, heavy truck ABS systems are commonly combined with traction control systems and stability control systems, which add more sensors and more ECU computing power to the mix. Bendix, for example, in adding both roll stability and yaw stability to its ABS 6 product, installs a steering angle sensor to the steering column, a yaw rate and lateral acceleration package, pressure sensors, to keep track of what the driver is doing with the brakes, and an ECU with more power.

"That requires technicians to acquire a little more knowledge, but if you can troubleshoot an ABS system, you can troubleshoot a stability control system," says Weed. "But there are a couple additional components added, so mechanics need to stay up on the latest."

ABS is also well-suited for telematics capabilities, which allow a properly-equipped truck to use wireless communications to relay logistics, vehicle performance and maintenance information in real time to a computer at the main office or the maintenance shop.

A further twist could be in store in 2007 heavy-duty trucks, as higher underhood temperatures could affect air compressors.

According to Reid, "As we raise underhood temperatures, the operating temperature of the compressor goes up, and a compressor has a tendency then to pass oil past the rings. That oil gets into the air brake system, and the oil can attack rubber components inside the valve."

"We have a very good cross-functional team that is analyzing this issue," says Weed. "They are working directly with our customers, conducting tests to understand what, if any, effects we're going to see in our products from this higher operating temperature."


According to MeritorWABCO's Williams, the primary reasons technicians don't do thorough ABS troubleshooting are:

  • Tendency to take the path of least resistance
  • Lack of familiarity with the system
  • Lack of training

Add to that list the very real possibility that technicians don't have adequate tools available in the shop: "I still go into shops where I will ask a technician to go get a voltmeter, and they get a blank stare on their face," says Reid. "Yes, you still find some technicians that don't have the proper equipment."

The challenge for fleet maintenance managers, then, is to get technicians to go through the proper diagnostic steps, and not simply change parts and hope for the best.

Today, technicians can diagnose ABS faults by reading the system's internal blink codes, by hooking a hand-held diagnostic tool to the ABS data port, or by using PC-based software. Some tools are multi-mode, such as Nexiq's Brake-Link, a hand-held scan tool for trailer ABS that also interfaces with OEM diagnostic software on a shop PC.

"I think there will probably always be a need for all three types of diagnostic devices," says Bendix's Weed. "As electronic modules on commercial vehicles become more complex—not just for ABS but also, for instance, for an engine or transmission—I think that there's a good chance that you'll see more of a move towards PC-based diagnostics, because that provides your highest level of diagnostic support. That would be PC-based software that you would procure from the software provider and load it onto the laptop and use that to troubleshoot the system.

"The diagnostic software will guide the technicians to inspect the wheel end, and tell them what to look for," he adds. "In the case of an open or a shorted wheel speed sensor, the diagnostic software will actually show a picture of the connector and identify the terminals, and direct the mechanic to connect an ohmmeter, for example, to take a resistance check, and (tell him) what he should get. It's a pretty powerful tool, no doubt about it."


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