What Does The Eco Mode On Your Car Do?

An increasing number of new vehicles come equipped with an ECO mode selector which drivers can activate when they want to conserve fuel and stretch their ringgit while travelling on the roads.

It seems simple enough but there are still misconceptions about what exactly the ECO button does. In addition, it doesn’t help that manufacturers all have slightly different ways of referring to them – BMW calls it ECO PRO, while Honda fits a cute little green button with the words ECON on it… but they all basically work the same way.

So what does it actually do?

In the early 90s, as cars got increasingly electronic, Engine Control Units or ECUs started to take the place of older, less precise mechanical systems. As ECUs got more powerful and intelligent, they were used to control a wider range of vehicle functions.

In today’s cars, the ECU controls everything from the engine, gearbox, steering system, active safety systems, even the air-conditioning, making it sort of the central brain of the vehicle.

Hence, simply changing the way the ECU “thinks”, can alter the overall performance of the vehicle. This is where the ECO mode comes into play.

The ECO button in most modern vehicles controls four basic systems of the car to reduce fuel consumption.

Notwithstanding, more advanced drivetrains such as Hybrids and Plug-In Hybrids will have a wider range of applications under the ECO mode, this article focusses on the basic functions of the ECO mode, which are found in most modern petrol, and diesel-powered cars.

ECO Mode changes the throttle response of the vehicle

When the ECO mode is engaged, the manner in which the engine takes in air (via the throttle body valve) is controlled in an effort to save fuel.

Hence, there is less performance and engine response but better control over how much air and fuel goes into the engine for combustion.

ECO Mode changes the way your transmission shifts gears

When in ECO mode, the ECU will deliberately instruct the transmission to shift up into a higher gear sooner to let the engine settle into a cruise and save fuel. 

It will also restrict the transmission from shifting down - which will need the engine to work harder and burn more fuel - unless absolutely needed, like in the case of climbing a hill or overtaking.

ECO Mode alters the response of the cruise control system

In cars with a cruise control feature, ECO mode combines the efforts of the first two features to cruise at the desired speed of the driver while using the least amount of fuel.

In the "Normal" driving mode, the cruise control system will do its best to maintain the desired speed at all times. In ECO mode, fuel efficiency is prioritised instead of maintaining the desired speed, hence the cruising speed might fluctuate slightly in an effort to conserve fuel.

When possible, the Cruise Control will gradually increase/decrease the car's speed back to its pre-set cruising speed.

ECO Mode augments the car's Air-Conditioning (AC) system

A significant amount of the engine's power is used to drive the AC system, hence, simply turning down the AC system can help save fuel. 

In ECO Mode, the car’s AC system's performance is reduced – so instead of operating at 100 percent, the system is made to work at 70-80 percent to reduce the amount of power it drains from the engine.

Of course, the air-conditioning will not be as cool as when in the "Normal" driving mode, but in most conditions, the reduction in coolness is hardly noticeable.

Some cars have an ECO Indicator instead...

In certain vehicles – such as the new Perodua Myvi – there is no ECO mode button, rather an ECO Indicator.

The ECO Indicator (Proton has a similar function called the ECO Driving Assist), monitors a few vehicle parameters such as selected gear and vehicle speed and lets the driver know he/she is driving in a fuel-efficient manner. 

If the driver drives in an aggressive fashion, i.e.: accelerating/braking abruptly, the ECO indicator light switches off to denote that the car is now using more fuel.