Traction control is just that – a system detects when the some wheels have lost traction and takes steps to counteract this wheelspin. It uses a computer and the same sensors used for the anti-lock brakes. The traction control system (sometimes known as TCS) sensors work by measuring the rotational speed of the driven wheels, comparing them to each other, and even the non-driven wheels.
When driving in a straight line on dry pavement, all of the wheels should be turning at exactly the same speed, and if the computer detects a certain percentage difference it will step in in one of several ways. The newer the car the more complex the system will be and the more options the computer will have for improving traction, from limiting engine power, to applying the brakes on one or more wheels. On some cars the traction control only monitors the two (front or rear) driven wheels, but on more advanced systems, and cars with all wheel drive, it keeps an eye on all four wheels. In the past 15 years, more and more TCS is also tied into stability control systems to help limit spins and skids.
When you hit a low-grip surface, or accelerate too aggressively, you may notice a flickering light or warning message on the dashboard, which shows the traction control is operating. The aim is to reduce tire slippage and increase traction, for example on muddy or leafy surfaces.
However, traction control can do more harm than good In some situations, for example in snow or sand, where both/all driven wheels slip when moving off from a standstill. The simpler systems may try to cut the engine power too much, especially when the tires slip under the slightest throttle. The resulting intervention can make progress very difficult, so most cars have a button to turn off the TCS or at least set it to allow much more wheelspin than is normal. Some cars don’t allow you to deactivate the traction control completely, but do have a setting for snow or ice.
Brake-based systems tend to work by slightly applying the brakes to one driven wheel. Some vehicles even combine a mechanical, viscous, or clutch-based limited-slip mechanism with computer-controlled brake and power cutting-based traction control, for an almost unstoppable system on any surface. But remember, you are still limited by the grip of your tires when it comes time to apply the brakes, or negotiate a corner.
However, if you regularly drive in snow or sub-zero conditions, you'd be wise to keep strips of old carpet or kitty litter in the trunk to put beneath the driven wheels to get going in extremely slippery situations. Snow socks are also a good alternative to get you moving in slippery conditions. For really serious winter excursions, and because the law may insist, you may need to pack some tire chains before you drive in the mountains in the winter.
Traction control problems are rare but are usually indicated by the traction control warning light (which should appear briefly when you start the engine and then goes out) coming on. You can still drive the vehicle, but should take care in adverse weather conditions. Typically it is caused by a bad ABS or wheel speed sensor, but it can also be caused by a tire being extremely low on air, and may come on when switching to the mini spare tire because of the difference in diameter.