A car’s traction control system uses a computer and the same sensors used for the anti-lock brakes to detect a difference in the speed of the wheels on the car. But instead of working to limit wheel lock-up when applying the brakes, traction control uses various methods to stop the wheels from spinning when you’re accelerating. 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 is 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’s all four wheels. In the last 15 years, more and more TSC are also tied into stability control systems to help maintain traction when going around a corner to limit spins and skids.
When you hit a low traction 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.
In certain situation, traction control can do more harm than good, 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 wheel spin 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 better by slightly applying the brakes to one driven wheel, sending power to both wheels almost as well as if you had a limited slip differential. 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.
Even with traction control, if you regularly drive in the snow or below freezing conditions, something like strips of old carpet or kitty litter should be kept in the trunk to deploy beneath the driven wheels to get going in extremely slippery situations. For really serious winter excursions, and because the law may insist, you may need to pack some tire chains before you drive in the mountain 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.