Why doesn't the cars start-stop system work and how do you fix it

The car's start-stop system is one of the mechanisms currently in modern-day vehicles to reduce fuel consumption and emissions. This system works by automatically shutting down and restarting the internal combustion engine of the car. Thus reducing the time spent by the engine idling away.

As we already mentioned, failure for the start-stop system of your vehicle to kick in during that latency period of the engine would cause fuel wastage. It will also cause a high level of emissions being let out into the environment.

start-stop system

The car's start-stop system[/caption]This is why it's important that the car's start-stop system is working effectively. However, there have been cases where this system stops working as efficiently as it ought to.

That's why in this article, we'll be discussing why your car's start-stop system might suddenly stop working. And also how you can fix it. You can also find out how to disable auto start/stop.

How does the vehicle's start-stop system work?

In modern cars, the engine isn't the sole mechanism responsible for the running of the automatic vehicle. There are mechanisms and devices built into the engine that sends messages to the control unit of the engine.

This helps the engine work effectively in making sure the car works at optimum performance. Now how does the car's start-stop system work? It works with the car's main computer.

how does the car start-stop system work

The start-stop system[/caption]It detects if the car is stationary or you're pushing the brake pedal down. This depends on if it's a gear shift or automatic. The car's start-stop system will then tell the car to stop delivering fuel to the vehicle's cylinders.

As soon as the system notices that the car is about to start moving again either by the driver releasing their feet on the gas pedal or the car is about to dip the clutch, the ignition starts again without the driver necessarily doing anything to kick-start the engine.

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Reasons the cars start-stop system might not be working

There are actually several reasons why your vehicle's start-stop system might not be working. And most times, it doesn't actually have anything to do with a fault in the engine of the vehicle. Rather it's the fault of the environment.Here are some reasons why this mechanism might not be working:

Wrong battery quality

Due to the requirements the automatic car's start-stop system needs, a  lot of innovation was put in creating the battery that would be best for the effective functioning of the vehicle's start-stop system. These batteries were created to generate enough electricity to power every intrinsic and intricate functioning of the vehicle.

However, in the case that the wrong battery was fixed in your vehicle, the amount of power generated by the battery will be insufficient. This will cause the battery to deteriorate over time because of the load exerted on it and as a result, the car's start-stop system will either rarely or never switch off the car's engine.

Safety reasons

A Reason unrelated to the car's Engine of why your car's start-stop system might not be working is reasons relating to driver and passenger safety.Of course, this safety measure works differently from other safety measures e.g anti-theft. The anti-theft safety measure you can know more about in this article.

The modern-day vehicles weren't just created for a smoother and easier driving experience, but rather, the safety of those within the vehicle and other road users were taken into consideration.

For example, the vehicle's start-stop system might fail to work if the car's passengers haven't engaged their seatbelts. Also, the car's start-stop system won't work at all if the driver's car door is open or the hood of the vehicle is open.These measures were put in place by vehicle manufacturers to ensure the safety of the borders in the vehicle and not just the driver, the passengers as well.

Too high engine temperature

A Reason for the lack of efficiency of your car's start-stop system or for this system to stop working entirely is a high temperature in the engine. If your car's engine is just too hot it might need some time to cool down and go back to its optimum performance temperature before the car's start-stop system can go back to normal.

However, in the case of overheating your vehicle, then proper diagnosis by a professional technician would be the best course of action.

Too low engine temperature

The same thing with when the temperature of the engine is too high, when the engine temperature is too low, your vehicle might need to go through a warming period to heat itself up in order to kick start its start-stop system.

The optimum temperature of modern-day engines of vehicles to run is between 195 degrees to 220 degrees. Anything lower than 195 degrees will just not be sufficient in running the vehicle's engine.

Environmental temperature

Environmental temperature actually has a lot to play in the effectiveness of the car's start-stop system. In fact, the environment is one of the major causes of the car's start-stop system not working as effectively as it ought to.

When the outside environment is hot or cold and if you have either the car's heating system or air-conditioning system turned on as the case may be, your car might notice the use of these functions and may decide to leave them running.

This doesn't mean that your car's start-stop system doesn't work anymore, it just means your car is letting the basic functions you might need for your comfort run instead of turning them off just because the vehicle is not in motion.


The car's start-stop system might not engage when you're driving on a sloped area or climbing up a hill. This has a lot to do with safety as your car engine going off when you're making your way up a hill might be detrimental to the lives of the passengers in the vehicle and other road users.

Also, it would prove frustrating and time-consuming to have your car continuously going off when you're trying to make your way up a steep slope.

Certain car functionings are active

As a function found in all modern vehicles, the car's start-stop system might fail to work if the car senses another smart mechanism of the car is also working.An example would be if the parking assistant of the car is active. In this case, the car's start-stop system cannot function effectively until the parking assistant is no longer in use.

BMW Parking Assist

This is essential as if you're using this system when you're trying to park your vehicle, it might make the experience even more tasking than it already is.

Faulty battery sensor

Car sensors are responsible for the monitoring of data that keeps the car running. A car sensor that is bad or malfunctioning will not be able to send the necessary information to the engine to engage the vehicle's start-stop system.

That means the car won't be able to detect when it's time to engage the start-stop system .In this case, it's important that you get in contact with a professional technician. Because this calls for repairs or total replacement.

How to fix the cars faulty start-stop system

Sometimes when the car's start-stop system is not working as it should be i.e it's refusing to activate or it's idling, the problem might be that there's no actual problem. Instead, your car might need some time to get to its optimum performance temperature of the engine.

This will enable the car's system to activate.The important thing is to wait it out.Another reason for this car system to not be working could just be a safety issue. And you need to get to more level terrain shut the driver's door or engage seatbelts.But in the occurrence that;

  • Your engine has heated up
  • None of your vehicle smart assistants are engaged
  • You're not driving on a slope or you're driving at 20m/h
  • And your start and stop system is still acting up,

Then your vehicle's start-stop system might need professional fixing. As drastic as it might seem, taking your vehicle to see a professional technician will help in fixing the issue. It could probably be that the battery requires replacing or other related issues. A mechanic can help you in fixing that.


Modern cars come with highly effective and efficient sensor systems and mechanisms that help your job as a car user/owner so much more easy and simple. And of course one of those systems is the car's start-stop system. It detects when your car's engine should be idle. It also detects when the power output should increase.

That is when it's time for your vehicle to be running without you needing to turn on the ignition and go through the tedious process of getting your car in motion.

Aside from how much easier, it is to use a car now, the car's start-stop system has made fuel management, and efficiency so much better as you're less likely to over-consume fuel and there'll be fewer emissions. Thus saving you on gas money while still taking care of the environment.

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