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ABS Diagnostic Equipment

August 6, 2009

Antilock brake systems have been around since the 1980s, so many ABS-equipped vehicles have accumulated enough miles to start experiencing ABS problems. Internal corrosion is a leading cause of trouble in ABS hydraulic modulators, while electrical faults in wheel speed sensor circuits and pump motors can prevent the system from functioning properly. Leaky high-pressure accumulators are another common problem.


All ABS systems run self-diagnostic tests when the vehicle is driven to check for faults. If a fault is detected, it will usually set a code and turn on the ABS warning light to alert the driver. On most applications, the code and warning light will also temporarily disable the ABS system (and traction control and/or stability control systems if the vehicle also has these features).


Finding out why the ABS light is on requires plugging a scan tool into the diagnostic connector to read out the code(s). A few of the older vehicle applications have manual flash codes that do not require a scan tool, such as older Chevy, Ford and Dodge pickup trucks with Kelsey-Hayes rear wheel ABS. Jumping or grounding the specified pins on the diagnostic connector is usually all that’s required to flash out the codes. But on most late-model vehicles, a scan tool is required to read ABS, traction control and stability control fault codes.


Most do-it-yourself and entry-level grade aftermarket scan tools that can read powertrain codes lack the ability to access ABS codes (but there are exceptions). They are primarily designed to read and clear OBD II engine and transmission codes, not ABS codes or other body-related codes.


What’s more, most DIY scan tools and entry-level scan tools do not have bidirectional communications capabilities. This means the scan tool can only read and display codes and other PIDs (performance information data), but it can’t activate anything, run anything or initiate any self-diagnostic tests. Factory scan tools and most professional-grade scan tools, by comparison, do have bidirectional communications capabilities and can run many self-tests that are provided by the vehicle manufacturer — but only if the scan tool has the right software. For ABS diagnostics, that means software that can read and access the ABS system. If the capabilities of the software are limited, or the software is out-of-date, the scan tool may not be able to access any ABS codes or run any ABS self-tests.


ABS codes and self-tests require additional software that goes beyond what is needed to read and interact with OBD II system data. If you are doing mostly engine diagnostic work, then all you need is a scan tool that can do powertrain diagnostics. Consequently, scan tool manufacturers have historically limited the capabilities of their DIY and low-cost, entry-level tools to powertrain only. However, recently Innova has added the ability to read ABS codes to its 3150 CanOBD2 scan tool.


On most professional-grade scan tools, ABS software is still offered as an extra-cost, add-on module or upgrade. Or, the scan tool manufacturer sells the ABS software packaged with a dedicated ABS tester or scan tool.
Actron makes a dedicated ABS code reader (model CP9449) that sells for less than $300, which is handy for reading and clearing codes. Though targeted primarily to the DIY market, professionals can also use this tool for quick diagnostic checks.


If you only need a scan tool to read and clear ABS codes, either of these two tools can satisfy that need. But for more advanced diagnostic work, you will need either a factory scan tool, a professional scan tool with ABS software that can talk to the ABS system, or a dedicated ABS tester that can perform various self-tests such as cycling the ABS solenoids, running the pump motor and so on.


OTC’s 3416 ABS Reader II Vivid Color is a dedicated ABS tester that also allows access to the airbag system as well as global OBD II powertrain codes and PIDs. The Genisys-based tool offers coverage on domestic and Asian models up to model year 2008. It can be used for tire pressure monitoring systems, as well.
A scan tool has become a necessity for brake work on many late-model vehicles. The ability to cycle ABS solenoids (or hone the pistons in the case of a Delco VI ABS system) may be necessary when doing brake work or bleeding the brake lines on a vehicle that has ABS. Air may become trapped inside the ABS modulator if the ABS solenoids are not cycled while bleeding the brakes. Cycling may also be required to remove air if the ABS modulator, an ABS solenoid, brake line or other hydraulic component has been replaced. If your scan tool can’t do the job, you may not be able to finish the repair. Or, you may end up with a comeback and an unhappy customer because the brake pedal feels soft or has too much travel.


OEM Scan Tools vs Aftermarket Scan Tools
Factory scan tools can access any fault code or run any self-test that is accessible through the vehicle’s onboard electronics, be it powertrain, ABS, air bags, HVAC or anything else. But many technicians and shops feel they can’t afford to buy a separate scan tool for every make of vehicle they might have to work on. You can probably justify buying a factory scan tool for your most common applications such as Ford, GM, Chrysler, Toyota or Honda. But what about European makes such as Audi, BMW, Mercedes and VW? Some of these factory scan tools can be very expensive.


Aftermarket scan tools that can handle a broad range of makes and models provide a more affordable option. Most provide complete coverage for domestic makes, but import coverage (especially European applications) may be limited or only available in a special module.


Snap-on’s Fast-Track software for its Ethos, Solus, Modis and Verus scan tools provides ABS coverage on domestic models and Asian models, with European coverage available in their 9.2 software bundle.
Always check with the scan tool manufacturer for what vehicle applications their ABS software covers. This may require a call to their technical services department as some of this information is not readily provided on their corporate websites or product brochures.


You also need test equipment that can check the operation and performance of wheel speed sensors (WSS), which are the most common cause of ABS faults. Most wheel speed sensors are magnetic, and are vulnerable to a buildup of metallic debris from brake rotors and pads that weaken the signal. Cracks, rust or damage on the sensor tone ring can also interfere with the signal produced by the sensor, causing the ABS system to set a code and shut down. Excessive bearing play in hub units with built-in sensors can cause similar problems. Wiring faults in the wheel speed sensor circuits are also common due to vibration, corrosion and road damage.


A dedicated wheel speed tester such as Waekon’s 20480 Antilock Brake System Wheel Speed Sensor Tester can be a real time-saver for diagnosing WSS problems. Otherwise, you’ll have to check the resistance of suspicious sensors with a digital ohmmeter, and/or their voltage output with a digital voltmeter. A digital storage oscilloscope can also be used to check the waveform signal from each wheel speed sensor, and a breakout box and DVOM come in handy for checking the integrity of the WSS wiring circuits.


Waekon also makes a BEQ0397 ABS and Brake Pressure Test Kit that includes a pair of pressure gauges for checking the amount of brake pressure exerted at the calipers. This tool can be used to diagnose a brake imbalance problem that is causing a brake pull to one side, or an inoperative or restricted brake circuit.

 

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