What stop-and-start does and why cars have it

Stop-and-start is a feature that automatically shuts off your engine when you come to a complete stop — at a red light, in traffic, or waiting in a drive-through — and restarts it the moment you release the brake pedal or press the accelerator. The system is designed to cut fuel consumption and emissions during idle time, which adds up over thousands of stops in city driving.

Most new cars sold today have this feature built in, though older vehicles do not. It runs in the background without you having to do anything. You will notice the engine goes quiet when you stop, then starts again smoothly when you move. Some drivers find the sensation jarring at first; others do not notice it at all.

The technology is standard on many brands — Toyota, Honda, Ford, BMW, Audi, and others all use versions of it. The names vary: Toyota calls it Eco Idle, Ford calls it Auto Start-Stop, BMW calls it Auto Start-Stop, and Audi uses the same name. The mechanics are slightly different between manufacturers, but the outcome is the same.

Key Takeaways

  • Stop-and-start automatically shuts the engine off when you stop and restarts it when you move, reducing fuel use during idle time.
  • You can turn the feature off using a button on your dashboard, usually labeled with an "A" with a circle around it, and it will stay off until you restart the car or manually turn it back on.
  • The system uses a reinforced starter motor and a larger battery than traditional cars to handle frequent restarts without wearing out faster.
  • Stop-and-start does not harm your engine or battery under normal conditions, though extreme cold or a weak battery can prevent it from working.

How to turn stop-and-start on and off

Most cars with stop-and-start have a button on the dashboard or steering wheel that lets you disable it. The button usually shows an "A" with a circle or slash through it. Press it once and the system turns off; the light on the button will go dark or change color. Press it again and it turns back on.

When you turn off the engine and restart the car, stop-and-start resets to its default state — usually on. If you turn it off every time you drive, you will need to press the button each trip. Some newer cars let you change the default setting in the vehicle menu, so the system stays off until you manually turn it back on, but this varies by model and year.

If you do not see a button labeled with the stop-and-start symbol, check your owner's manual or the vehicle's touchscreen menu. Some cars hide the control in the settings rather than on a physical button.

Why your stop-and-start might not be working

Stop-and-start will not set up if your battery is low or weak. The system needs enough charge to restart the engine reliably, so if the battery voltage drops below a certain threshold, the car disables stop-and-start automatically to preserve power for essential functions. A weak battery is the most common reason the feature stops working.

Cold weather also affects stop-and-start. In freezing temperatures, the engine needs more power to restart, and the system may not set up until the engine warms up. Some cars disable stop-and-start entirely in very cold conditions to avoid strain on the starter.

If the system is malfunctioning, you may see a warning light on the dashboard. This usually means a sensor has failed or the starter motor needs service. Take the car to a mechanic or dealership to have it diagnosed. Do not ignore the warning light, because it signals that something in the system is not working as designed.

Does stop-and-start wear out your engine or battery faster

Stop-and-start does not damage your engine under normal conditions. Manufacturers design the system with reinforced engine components and a larger starter motor that can handle thousands of restarts. The oil in your engine is still circulating and protecting the parts, so the frequent on-off cycles do not cause premature wear.

The battery does work harder with stop-and-start, but car makers install a larger or more robust battery in vehicles with the feature to handle the extra demand. Over the life of the car, the battery may wear out sooner than it would without stop-and-start, but this is factored into the design. A typical car battery lasts three to five years regardless; stop-and-start may shift that window slightly, but not dramatically.

The real wear risk comes from a weak or failing battery. If your battery is already struggling, stop-and-start can accelerate its decline because the system demands more from it. If you notice the feature is not working, have the battery tested before it fails completely.

How much fuel does stop-and-start actually save

The fuel savings depend on how much time you spend idling. In city driving with frequent stops, you may see a 3 to 5 percent reduction in fuel consumption. On the highway where you rarely stop, the savings are negligible because the engine is not idling long enough for the system to matter. In heavy traffic or stop-and-go commuting, the savings are more noticeable.

Real-world savings also depend on your driving habits, the outside temperature, and the specific car. A driver who sits in long traffic jams will see more benefit than someone who drives mostly on open roads. Cold weather reduces savings because the engine needs more fuel to warm up after each restart.

The system was designed primarily to meet emissions standards, not to save you money on gas. The fuel savings are a side effect, not the main goal. If you turn off stop-and-start because you find it annoying, the impact on your fuel bill will be small.

Stop-and-start in different driving conditions

In city driving and traffic, stop-and-start works constantly and provides the most benefit. Every red light, every traffic jam, every moment you are stopped with your foot on the brake triggers the system. This is where the feature was designed to work.

On the highway, stop-and-start rarely activates because you are not stopping. Even if you coast to a stop briefly, the system may not have time to shut down and restart before you accelerate again. Highway driving produces almost no benefit from the feature.

In very cold weather, the system may not set up at all, or it may set up less frequently. The engine needs more power to restart in freezing temperatures, so the car prioritizes battery charge for essential functions. In extreme heat, the system works normally but the battery may be under more stress.

When you might want to turn stop-and-start off

If you find the sensation of the engine shutting off and restarting unsettling, you can turn it off. Some drivers feel a slight jolt or hear a noise when the engine restarts, and if that bothers you, disabling the feature is a reasonable choice. There is no penalty for turning it off.

If your battery is weak or aging, turning off stop-and-start can extend its life by reducing the demand on it. If you are planning to replace the battery soon anyway, this may not matter. But if you want to squeeze more time out of an older battery, disabling the feature is one way to do it.

If you are towing a trailer or carrying a heavy load, some manufacturers recommend turning off stop-and-start because the extra weight puts more strain on the starter motor during restarts. Check your owner's manual for guidance specific to your vehicle.

Frequently Asked Questions

Does stop-and-start work when the air conditioning is on?

Yes, but the system may not set up if the air conditioning compressor is running at full load. When you stop and the AC is working hard to cool the cabin, the engine may stay on to power the compressor. Once the cabin reaches the set temperature, stop-and-start can set up normally.

Can I disable stop-and-start permanently?

No, you cannot permanently disable it without a software update or modification. Turning off the button disables it for that drive only. When you restart the engine, the system resets to its default state. Some dealerships can reprogram the car to keep it off by default, but this varies by manufacturer and may void your warranty.

What happens if the battery dies while the engine is off?

This is extremely rare because the system monitors battery voltage constantly. If the battery charge drops too low, the car disables stop-and-start automatically to preserve power. The engine will not shut off if doing so would leave you stranded.

Does stop-and-start affect my warranty?

No. Stop-and-start is a factory feature, and using it or disabling it does not void your warranty. If the system malfunctions, the manufacturer covers repairs under the powertrain warranty, which typically lasts five years or 60,000 miles.

Is stop-and-start the same as hybrid technology?

No. Hybrids use an electric motor to power the car during low-speed driving and shut off the gas engine entirely. Stop-and-start only shuts off the engine during idle and relies on the gas engine to move the car. Stop-and-start is simpler and cheaper than hybrid technology.