Why Does My Car Shut Off When I Stop?

I have driven thousands of cars throughout my life and was not aware my new car came with the auto start-stop feature. So, imagine my surprise while driving home from the dealership and thinking the engine was stalling every time I came to a red light. That surprise quickly turned into frustration when the engine restarted as soon as my foot came off the brake pedal.

As a 50+ year ASE and General Motors master technician and automotive technology vocational educator, I’m thinking, how can a technician fix a stalling problem when the engine restarts by itself? But then my automotive “Spidey-sense” kicked in. Before calling the dealershipand sounding like a foolI decided to read the number one best-selling unread book of all time: the owner’s manual.

This is where I first learned about auto start-stop. Read along to find out what you need to know about the start-stop system.

Why Does My Car Shut Off When I Stop?

If your car shuts off when you stop and then turns back on when you take your foot off the break, it is equipped with a start-stop system. The system is remarkably beneficial when driving in heavy stop-and-go traffic since It increases fuel mileage and reduces engine tailpipe emissions (smog). Frequent stops and long periods of idling can lead to significant fuel consumption, so vehicles equipped with start-stop technology come equipped with heavy-duty starter motors, engine components and batteries designed to deal with an engine frequently shutting off and restarting without causing premature wear to the starter motor or engine.

What Is the Stop-Start System?

When coming to a complete stop at a traffic light or while sitting in freeway traffic, the start-stop system turns the engine off. If your engine isn’t running, it’s not using any fuel, producing exhaust emissions or causing engine parts to wear. This increases fuel efficiency by saving fuel that would be wasted while sitting at idle. The engine automaticallyin my experienceinstantly restarts (the system was engineered to restart the engine in less than a half-second) as soon as you begin releasing the brake pedal, so you can continue driving without hesitation.

How To Reset the Stop-Start System

For any number of reasons, you may need to reset your start-stop system. First, it’s best to check your owner’s manual in case there are instructions specific to your make, model or year. Here are the generic steps:

• Battery: Disconnect the battery for five minutes.
  • Disconnecting the battery may cause you to lose any “pre-sets.” You may want to consider plugging a battery memory saver into your car’s power outlet or cigarette lighter to supply a bit of current, protecting the computer, radio, keyless entry, and clock memory settings from being erased.
• Scan Tool: Depending on your make, model and year, you may be able to reset the start-stop system with a scan tool. Scan tools can also clear ECM and other system’s error codes.

Why would I have to reset the start-stop system?

Unfortunately, there are a few reasons why you may have to reset the start-stop system, including:

• Battery: A weak, failed or shorted battery can keep the start-stop system from functioning properly.
• Battery cables: Loose or corroded battery cables and grounds can wreck the electrical system in today’s sophisticated, highly complex vehicles, whether electrified or internal combustion engine (ICE).
• Replacing components: Replacing the starter motor, alternator, or computer (or computer software upgrade) may result in lost communications between the start-stop system and the new parts, keeping the system from operating correctly.
• Start-stop system malfunction: Extreme temperatures, bad or failing engine and other sensors, part wear and tear, or glitchy software can cause errors with the start-stop system.
• Warning lights: Resetting the start-stop system may be necessary to turn off the warning light and restore normal system functions.

Do All 2024 Cars Have Stop-Start System?

No, there are a few, mostly sub-compacts, which forgo the start-stop function. For example, the Kia Soul, depending on the trim package, may not come with a start-stop feature. Also, hybrids and plug-in hybrids that have ICE employ a similar but slightly different start-stop system. This results in a smoother transition from battery power to gasoline power when starting from a stop. Full battery-powered electric vehicles do not use nor need a start-stop system.

Can I Turn Off the Stop-Start System?

Yes, if you find start-stop infuriating (as my wife does), virtually all vehicles with the start-stop function have either a button or switch that will temporarily disable the system.

Is it recommended that the Stop-Start System be turned off?

No, turning off the start-stop function is not recommended. Although the EPA may or may not include start-stop in how they determine a vehicle’s fuel miles per gallon estimates, depending on your driving habits, you may expect a 3-9% increase in fuel economy. Remember, an ICE releases “zero” tailpipe emissions when it’s not running.

Things to Consider When Using the Stop-Start System

Start-stop systems are purposely built for durability and are designed to withstand constant starts-and-stops that normally cause excessive wear on the started motor and ICE. If you are concerned about premature wear and tear, then disable it while driving.

Batteries in cars with start-stop technology take a beating. However, newer cars with high-demand electronics use either high-performance Absorbent Glass Mat (AGM) or Enhanced Flooded Batteries (EFB). These batteries are intentionally designed to manage constant discharging and charging due to start-stop. To reduce battery stress and load:

• Check and service the battery and battery cables/terminals regularly.
• Avoid letting your car sit for too long and minimize short trips.
• Turn off accessories, including the HVAC system, infotainment, and lights to keep them from drawing power from the battery.

Resources

• U.S. Department of Energy: “Why Is Fuel Economy Important” (Nov 2024)
• Edmunds: Do Stop-Start Systems Really Save Fuel? (Nov 2024)
• Battery Council International: “Start-Stop Vehicles Reduce Emissions & Boost Fuel Economy” (2024)
• Kia: 2024 Soul Owner’s Manual (20204)

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