What is traction control and how does it work?

Traction control is an almost universal feature of modern cars, and is particularly important for electric vehicles

Traction control

Traction control (sometimes referred to as 'TC' for short) has been mandatory on every new car sold in Europe since 2011 and had become a common feature long before that date. It's a vital safety system that helps prevent innumerable crashes every day, but as long as it's working properly, most drivers are hardly aware it's there, so it's easy to take for granted.

The main function of traction control is to prevent something called 'wheelspin'. We're all familiar with the moments in old movies when somebody jumps into a car and speeds off amid squealing tyres and smoke, but traction control prevents this happening in the first place.

Wheelspin occurs when there's too much power being sent to a car's tyres, so instead of gripping the road steadily and evenly, the slip and slide across it, often turning much faster than the car is moving. Wheelspin can also occur when a tyre comes into contact with a low-grip surface, such as loose gravel or ice, even momentarily.

When the wheels spin like this, there's a danger of the driver losing control of the car: the back end can spin around (which is also known as 'oversteer'), or the front end can 'push' straight on instead of following the driver's desired path around a corner (which is also known as 'understeer').

When was traction control introduced?

The very first traction-control systems appeared during the 1970s, but it was the late 1980s and early 1990s when the technology became truly effective and widespread. High-end models like the BMW 7 Series and Mercedes S-Class were the first to get traction control, but as the cost of the technology came down it began to appear in more humble family cars and superminis.

How does traction control work?

Traction control and other electronic driver aids have become increasingly complex and sophisticated in recent years, but in its most basic form, a traction-control system incorporates a sensor that detects how fast each of the car's wheels is spinning. If it senses one wheel is spinning a lot faster than the others (indicating a loss of traction), a signal is sent to the engine electronics requesting that power be reduced so the wheel can regain grip, regardless of whether the driving is pressing the accelerator.

To the driver, this can feel like a momentary hesitation in power delivery, or even a misfire, but it can happen in the blink of an eye and often the only clue the system has engaged is an orange or yellow warning light on the dashboard blinking for a second or two.

The latest traction-control systems incorporate an additional element, known as Electronic Stability Control (ESC) or Electronic Stability Programme (ESP). This goes one step further than cutting engine power and can apply the brakes to the individual wheel or wheels that have lost grip. It can also boost engine power to the wheel or wheels that do have grip, helping to bring the car back under control.

Traction control

How do I know the traction control is working in my car?

As mentioned above, there's a warning light in the dashboard (usually with the symbol of a car and two 'skid lines' under it) that briefly flashes when the traction-control system comes into play. If it's already on when you start the engine, and stays on, then there's a fault with the system.

In this case you should take your car to a dealership without delay so the problem can be diagnosed and rectified. A traction-control warning light being permanently on will also cause your car to fail its MoT if it's due.

Should I ever turn the traction control off?

Generally speaking, no. The system can react faster than you ever will if the car loses grip on snow, ice, gravel or spilled fuel on an otherwise-clear road, so for safety it's advisable to keep it turned on nearly all the time.

However, if you're trying to pull away or make progress slowly on some particularly icy or muddy ground, it can be helpful to turn the system off temporarily, as a degree of wheelspin can help the car to get moving in such situations – as long as you're gentle with the accelerator. Consult your car's owner's manual for how to do this, and make sure you reactivate the system when you're back on solid ground.