On The Road

Stabilizing trouble with traction control

Dynamic stability traction control (DSTC) and other traction control systems may be the most important features on your car to have working properly in the winter months.

Last month we had a new customer bring in her 2012 Volvo XC60 3.2L because she said her DSTC warning light went on and her electric emergency brake was not working correctly. She said that ever since the DSTC light came on, she wasn’t able to release or operate the emergency brake properly while the car was running. If she turned the car off, the emergency brake worked.

Essentially, DSTC is the antilock-brake system (ABS) and traction control put together. The purpose of DSTC is to keep the car from sliding, spinning and skidding. Traction control was designed to take power away from a wheel that starts to spin (slip) and transfer it to the opposite wheel of the same axle. Spin control is designed to prevent the wheels from slipping under acceleration. Spin control kicks in when the car is in conditions such as ice and snow. The system also can engage and disengage the brake calipers quickly to mitigate wheel slippage under braking.

It does all of this with sensors that measure the speed of each wheel, position of the steering wheel, position of the brake pedal, position of the accelerator pedal and a yaw-rate sensor (which measures a car’s angular velocity around its vertical axis).

Diagnosing the problem

While testing the DSTC system, we confirmed the customer’s complaint. We then connected the scanner and pulled several codes pertaining to the ABS hydraulic unit.

The DSTC codes came back right away. We cleared codes and ran the test plan. We saw the basic voltage and communication to the brake control module but could not see activity in the module. We also could not communicate with the emergency brake control module at all.

Because there is nothing to repair in the brake control module, the next step is to replace it. The brake control module is the brain of the ABS hydraulic unit/DSTC. Because this entire system works in a control area network, we surmised that the brake control module was pulling down the emergency brake module. One way we validated this theory was that when we turned off the car, the brake control module shut down and the emergency brake worked fine.

We replaced the ABS hydraulic unit (brake control module/ABS pump) and performed the bleeding procedure on the pump. We then had to load the new software into the brake module and code it. Once we were done, we ran the end-of-line test – and the system works to specification.

DSTC’s main job is to look out for and protect the driver at all times. A cool feature of DSTC is when the car is in sport mode: If it is being driven aggressively and the steering wheel and accelerator pedal inputs are meeting the computer’s specification, DSTC will enable the car to handle or corner at a superior level.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email [email protected] or visit sunnyvaleforeigncar.com.

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