Traction control helps a vehicle’s drive wheels maintain traction during acceleration.
What Traction Control Is Not
Traction control is not to be confused with electronic stability systems or antilock braking systems. Though these three systems are related and rely on some of the same sensors and other hardware, traction control is about maintaining acceleration; ABS maintains traction and the ability to steer during braking; and stability systems are a more recent development that help keep the car moving in the intended direction by preventing lateral sliding and yaw.
How Traction Control Works
When the drive wheels lose traction, due to a slick road surface or the proverbial lead foot on the accelerator, the vehicle doesn’t move forward as quickly as the driver would like, and it may slide to one side or the other. Traction control systems use a computer to monitor wheel rotation. If a wheel loses traction, the computer does one or more of the following:
- Applies controlled antilock braking to the slipping wheel(s), which transfers power to the other drive wheel or wheels
- Clamps down on the fuel supply to the engine (throttle), lowering engine power, even if the driver floors the accelerator pedal
In a two-wheel-drive vehicle, typically the ABS is used to slow one spinning drive wheel, sending power to the other as a limited-slip differential would, and the engine limiters kick in only if both drive wheels are spinning faster than the passive wheels, indicating that both drive wheels have lost traction and should be slowed to prevent freewheeling.
Traction-control system effectiveness -- and intrusiveness -- varies from make to make and model to model, but it definitely does the job and has improved markedly since its introduction. Earlier examples predated the proliferation of electronic throttle control and limited power the only way they could -- awkwardly -- by interfering with the ignition system or fuel injectors. Early objections to traction control were that they were too conservative, calibrated to clamp down on the slightest amount of wheelspin, which could result in a whole lot of noise but the car making little forward progress. Allowing some degree of wheelspin can help a vehicle “paddle” out of sand or loose snow, so nowadays traction control may be a bit less restrictive. When vehicles offer a dedicated driving mode for snow, this principle is often applied with traction control programming customized for that use. Likewise, off-road vehicles that have multiple driving modes sometimes apply different traction control programs for different surfaces.
ABS-based traction control has become effective enough that it now serves the same purpose as limited-slip differentials in some four-wheel-drive vehicles, saving much weight, complexity and cost.
How to Use Traction Control
Almost without exception, traction control can be turned off, and you might do so if you find you’re not making progress on a low-friction surface, especially in an older car. It can help rock a stuck car out of a snow bank, for example. In cars with stability systems, you can usually deactivate the traction control aspect alone by pressing the button briefly and looking for an indicator on the instrument panel. (The button often shows a car sliding and the indicator may show the same and/or read “trac off.”) Only if the button is held for several seconds will some vehicles allow the stability system also to be turned off.
If a car has traction control, it also has ABS, and if it has a stability system, that means it has all three. They became required standard equipment for all new passenger vehicles (below a 10,000-pounds gross vehicle weight rating) in the 2012 model year in the U.S.